Fluorolucent magnetic field generator

ABSTRACT

A transmitting element for generating a magnetic field for tracking of an object includes a first spiral trace that extends from a first outer origin inward to a central origin in a first direction. A second spiral trace can extend from the central origin outward to a second outer origin in the first direction. The second spiral trace can extend from the central origin to the second outer origin in the first direction. The first spiral trace and the second spiral trace can be physically connected at the central origin to form the fluorolucent magnetic transmitting element and at least a portion of the first spiral trace overlaps at least a portion of the second spiral trace.

BACKGROUND a. Field

The instant disclosure relates to a fluorolucent magnetic fieldgenerator and related components.

b. Background Art

Medical devices, catheters, and/or cardiovascular catheters, such aselectrophysiology catheters can be used in a variety of diagnostic,therapeutic, mapping and/or ablative procedures to diagnose and/orcorrect conditions such as atrial arrhythmias, including for example,ectopic atrial tachycardia, atrial fibrillation, and/or atrial flutter.Arrhythmias can create a variety of conditions including irregular heartrates, loss of synchronous atrioventricular contractions and stasis ofblood flow in a chamber of a heart, which can lead to a variety ofsymptomatic and asymptomatic ailments and even death.

A medical device can be threaded through a vasculature of a patient to asite where the diagnostic, therapeutic, mapping, and/or ablativeprocedure to diagnose and/or correct the condition is performed. To aidin the delivery of the medical device to the site, sensors (e.g.,electrodes) can be placed on the medical device, which can receivesignals that are generated proximate to the patient from a device (e.g.,electromagnetic field generator). Based on the received signals, anorientation and/or position of the medical device can be computed.

SUMMARY

Various embodiments herein provide a fluorolucent magnetic transmittingelement for generating a magnetic field for tracking of an object. Thefluorolucent magnetic transmitting element includes a first spiral tracethat extends from a first outer origin inward to a central origin in afirst direction. A second spiral trace can extend from the centralorigin outward to a second outer origin in the first direction. Thefirst spiral trace and the second spiral trace can be physicallyconnected at the central origin to form the fluorolucent magnetictransmitting element and at least a portion of the first spiral trace isoverlapped with at least a portion of the second spiral trace.

Various embodiments herein provide a fluorolucent magnetic transmittingelement for generating a magnetic field for tracking of an object. Afirst fluorolucent magnetic transmitting element can be disposed in afirst plane. A second fluorolucent magnetic transmitting element can bedisposed in a second plane. The second fluorolucent magnetictransmitting element disposed in the second plane can partially overlapthe first fluorolucent transmitting element disposed in the first plane.

Various embodiments herein provide a frame that includes a magnetictransmitting assembly. The frame can include a fluoro window. A firstplurality of magnetic transmitting elements can be disposed on the frameon a first side of the fluoro window. A second plurality of magnetictransmitting elements can be disposed on the frame on a second side ofthe fluoro window. The second side can be disposed on an opposite sideof the frame from the first side.

Various embodiments herein provide a method for preventing coil to coilcoupling in an array of magnetic transmitting elements. A referencesignal can be provided to a magnetic transmitting element and a low passfilter in parallel. The reference signal that has passed through themagnetic transmitting element can be sensed. A direct current offset canbe generated with respect to the reference signal via the low passfilter. An attenuation signal can be generated by summing the directcurrent offset and the reference signal that has passed through themagnetic transmitting element. The attenuation signal can be applied tothe reference signal to attenuate the reference signal.

Various embodiments can include a high frequency fluorolucent magnetictransmitting element drive circuit. The drive circuit can include avoltage input coupled to a Howland current source. The Howland currentsource can include an operational amplifier with an inverting input ofthe operational amplifier electrically coupled between a first andsecond modified Howland resistor and a non-inverting input of theoperational amplifier electrically coupled between a third and fourthmodified Howland resistor. The voltage input can be electrically coupledto the first modified Howland resistor. An output operational amplifierwith a non-inverting input can be electrically coupled to an output ofthe Howland operational amplifier of the modified Howland current sourceand an inverting input electrically coupled to the fourth modifiedHowland resistor. An output of the second operational amplifier can beelectrically coupled with a first resistor. A phase lead capacitor canbe electrically coupled between an output of the output resistor and thesecond modified Howland resistor. A fluorolucent magnetic transmittingelement can be coupled to the output of the output resistor.

Various embodiments can include a high frequency fluorolucent magnetictransmitting element drive circuit. A voltage input can be electricallycoupled to a low-pass smoothing filter, wherein an output of thelow-pass smoothing filter is electrically coupled to a non-invertinginput of an operational amplifier. Various embodiments can include amodified Howland current source, wherein the modified Howland currentsource includes a Howland operational amplifier with an inverting inputof the Howland operational amplifier electrically coupled between afirst and second modified Howland resistor and a non-inverting input ofthe Howland operational amplifier electrically coupled between a thirdand fourth modified Howland resistor, and wherein an output of theoperational amplifier is electrically coupled to the first modifiedHowland resistor. An output operational amplifier with a non-invertinginput can be electrically coupled to an output of the Howlandoperational amplifier of the modified Howland current source and aninverting input can be electrically coupled to the fourth modifiedHowland resistor, wherein an output of the second operational amplifieris electrically coupled with an output resistor. A phase lead capacitorcan be electrically coupled between an output of the output resistor andthe second modified Howland resistor. A fluorolucent magnetictransmitting element can be electrically coupled to the output of theoutput resistor.

Various embodiments herein provide a method for determining anattenuation term for a signal produced by a fluorolucent magnetictransmitting element. The method can include driving the fluorolucentmagnetic transmitting element with a first signal at a first frequencyand a second signal at a second frequency to generate a first excitationsignal and a second excitation signal, wherein the first frequency islower than the second frequency. The method can include receiving afirst received signal and a second received signal with a computer, thefirst received signal and the second received signal having beengenerated upon receipt of the first excitation signal and the secondexcitation signal with a magnetic position sensor. The method caninclude filtering the first received signal and the second receivedsignal. The method can include determining an attenuation term for thesecond received signal at the second frequency based on the firstfiltered and received signal and the second filtered and receivedsignal.

Various embodiments can include a non-transitory computer readablemedium comprising computer executable instructions for determining anattenuation term for a signal produced by a fluorolucent magnetictransmitting element. The instructions can be executable by a processorto drive the fluorolucent magnetic transmitting element with a firstsignal at a first frequency and a second signal at a second frequency,wherein the first frequency is lower than the second frequency togenerate a first excitation signal and a second excitation signal. Theinstructions can be executable by a processor to receive a firstreceived signal and a second received signal with a computer, the firstreceived signal and the second received signal having been generatedupon receipt of the first excitation signal and the second excitationsignal with a magnetic position sensor. The instructions can beexecutable by a processor to determine an attenuation term for thesecond received signal at the second frequency based on the firstreceived signal and the second received signal. The instructions can beexecutable by a processor to apply the attenuation term to filter theattenuation term to provide a filtered attenuation term.

Various embodiments can include a system for determining an attenuationterm for a signal produced by a fluorolucent magnetic transmittingelement. The system can comprise a processor and a non-transitorycomputer readable medium comprising computer executable instructions,the instructions executable by the processor to drive the fluorolucentmagnetic transmitting element with a first signal at a first frequencyand a second signal at a second frequency to generate a first excitationsignal and a second excitation signal, wherein the first frequency islower than the second frequency. The instructions executable by theprocessor to receive a first received signal and a second receivedsignal with a computer, the first received signal and the secondreceived signal having been generated upon receipt of the firstexcitation signal and the second excitation signal with a magneticposition sensor. The instructions executable by the processor todetermine an attenuation term for the second received signal at thesecond frequency based on the first received signal and the secondreceived signal. The instructions executable by the processor todetermine a position of the magnetic position sensor based on anattenuated received signal, the attenuated received signal having beengenerated through application of the attenuation term to the secondreceived signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts a diagrammatic view of an exemplary system forperforming one or more diagnostic or therapeutic procedures, wherein thesystem comprises a magnetic field-based medical positioning system, inaccordance with embodiments of the present disclosure.

FIG. 1B depicts a magnetic position sensor disposed on a medical devicefor use in the magnetic field-based medical positioning system of FIG.1A, in accordance with embodiments of the present disclosure.

FIG. 2 depicts a medical positioning system, in accordance withembodiments of the present disclosure.

FIG. 3A depicts a top view of a fluorolucent magnetic transmittingelement prior to being folded, in accordance with embodiments of thepresent disclosure.

FIG. 3B depicts an isometric side view of the fluorolucent magnetictransmitting element in FIG. 3A partially folded, in accordance withembodiments of the present disclosure.

FIG. 3C depicts a top view of the fluorolucent magnetic transmittingelement in FIG. 3A after folding, in accordance with embodiments of thepresent disclosure.

FIG. 4A depicts a top view of a magnetic transmitting array, inaccordance with embodiments of the present disclosure.

FIG. 4B depicts a side view of an insulation layer disposed between afirst layer of magnetic transmitting elements and a second layer oftransmitting elements, in accordance with embodiments of the presentdisclosure.

FIG. 4C depicts a top view of a first layer of magnetic transmittingelements of a magnetic transmitting array, in accordance withembodiments of the present disclosure.

FIG. 5A depicts a diagrammatic top view of a second embodiment of amagnetic transmitting assembly, in accordance with embodiments of thepresent disclosure.

FIG. 5B is a cross-sectional view along line ff of a magnetictransmitting element in an enclosure, which can be included in themagnetic transmitting assembly in FIG. 5A, in accordance withembodiments of the present disclosure.

FIGS. 5C to 5H depict x-ray sources and x-ray image intensifiers atvarious positions with respect to a patient's body, in accordance withembodiments of the present disclosure.

FIG. 6 depicts a top view of a third embodiment of a magnetictransmitting assembly, in accordance with embodiments of the presentdisclosure.

FIG. 7 depicts a schematic view of a first embodiment of a drive circuitfor a fluorolucent magnetic transmitting element, in accordance withembodiments of the present disclosure.

FIG. 8 depicts a schematic view of a second embodiment of a drivecircuit for a fluorolucent magnetic transmitting element, in accordancewith embodiments of the present disclosure.

FIG. 9 depicts a block diagram for a method for determining anattenuation term for a signal produced by a fluorolucent magnetictransmitting element, in accordance with embodiments of the presentdisclosure.

FIG. 10 depicts a graph showing a non-linear frequency-dependentattenuation of a signal generated by a magnetic position sensor due tothe presence of various metals with respect to free space, in accordancewith embodiments of the present disclosure.

FIG. 11A depicts a diagram of a system for determining an attenuationterm for a signal produced by a fluorolucent magnetic transmittingelement, according to embodiments of the present disclosure.

FIG. 11B depicts a diagram of an example of a computing device fordetermining an attenuation term for a signal produced by a fluorolucentmagnetic transmitting element, according to various embodiments of thepresent disclosure.

FIG. 12 depicts a schematic and block diagram view of an electromagneticnavigation system, in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

In some embodiments, and with reference to FIG. 1, a system 10 caninclude a medical device 12 and a medical positioning system 14. Themedical device 12 can include an elongate medical device such as, forexample, a catheter or a sheath. For purposes of illustration andclarity, the description below will be limited to an embodiment whereinthe medical device 12 comprises a catheter (e.g., catheter 12). It willbe appreciated, however, that the present disclosure is not meant to belimited to such an embodiment, but rather in other exemplaryembodiments, the medical device may comprise other elongate medicaldevices, such as, for example and without limitation, sheaths,introducers, guidewires, and the like.

With continued reference to FIG. 1, the catheter 12 can be configured tobe inserted into a patient's body 16, and more particularly, into thepatient's heart 18. The catheter 12 may include a handle 20, a shaft 22having a proximal end portion 24 and a distal end portion 26, and one ormore position sensors 28 mounted in or on the shaft 22 of the catheter12. As used herein, “position sensor 28” or “position sensors 28” mayrefer to one or more position sensors 28 ₁, 28 ₂, 28 ₃, . . . , 28 _(N),as appropriate and as generally depicted. In an exemplary embodiment,the position sensors 28 are disposed at the distal end portion 26 of theshaft 22 and can be impedance based position sensors (e.g., electrodes)and/or magnetic based position sensors (e.g., a wound coil, as depictedand discussed in relation to FIG. 1B). For example, the position sensor28 ₁ can be a magnetic based position sensor and the position sensors 28₂, 28 ₃, . . . , 28 _(N) can be impedance based position sensors. Thecatheter 12 may further include other conventional components such as,for example and without limitation, a temperature sensor, additionalsensors or electrodes, ablation elements (e.g., ablation tip electrodesfor delivering RF ablative energy, high intensity focused ultrasoundablation elements, etc.), and corresponding conductors or leads.

The shaft 22 can be an elongate, tubular, flexible member configured formovement within the body 16. The shaft 22 supports, for example andwithout limitation, sensors and/or electrodes mounted thereon, such as,for example, the position sensors 28, associated conductors, andpossibly additional electronics used for signal processing andconditioning. The shaft 22 may also permit transport, delivery, and/orremoval of fluids (including irrigation fluids, cryogenic ablationfluids, and bodily fluids), medicines, and/or surgical tools orinstruments. The shaft 22 may be made from conventional materials suchas polyurethane, and define one or more lumens configured to houseand/or transport electrical conductors, fluids, or surgical tools. Theshaft 22 may be introduced into a blood vessel or other structure withinthe body 16 through a conventional introducer. The shaft 22 may then besteered or guided through the body 16 to a desired location, such as theheart 18, using means well known in the art.

The position sensors 28 mounted in or on the shaft 22 of the catheter 12may be provided for use in a variety of diagnostic and therapeuticpurposes including, for example and without limitation,electrophysiological studies, pacing, cardiac mapping, and ablation. Inan exemplary embodiment, one or more of the position sensors 28 areprovided to perform a location or position sensing function. Moreparticularly, and as will be described in greater detail below, one ormore of the position sensors 28 are configured to provide informationrelating to the location (e.g., position and orientation) of thecatheter 12, and the distal end portion 26 of the shaft 22 thereof, inparticular, at certain points in time. Accordingly, in such anembodiment, as the catheter 12 is moved along a surface of a structureof interest of the heart 18 and/or about the interior of the structure,the position sensor(s) 28 can be used to collect location data pointsthat correspond to the surface of, and/or other locations within, thestructure of interest. These location data points can then be used for anumber of purposes such as, for example and without limitation, theconstruction of surface models of the structure of interest.

For purposes of clarity and illustration, the description below will bewith respect to an embodiment with a single position sensor 28. It willbe appreciated, however, that in other exemplary embodiments, whichremain within the spirit and scope of the present disclosure, thecatheter 12 may comprise more than one position sensor 28 as well asother sensors or electrodes configured to perform other diagnosticand/or therapeutic functions. As will be described in greater detailbelow, the position sensor 28 can include a pair of leads extending froma sensing element thereof (e.g., a coil) that are configured toelectrically couple the position sensor 28 to other components of thesystem 10, such as, for example, the medical positioning system 14.

FIG. 1B depicts a magnetic position sensor 28 ₁′ disposed on a medicaldevice 10′ for use in the magnetic field-based medical positioningsystem of FIG. 1A, in accordance with embodiments of the presentdisclosure. The magnetic position sensor 28 ₁′ can be a wound magneticcoil that is disposed along a shaft 22′ of the medical device 10′. Insome embodiments, the magnetic position sensor 28 ₁′ can be disposedaround an exterior of the shaft 22′, as depicted. However, although notdepicted, the magnetic position sensor 28 ₁′ can be disposed within aninterior lumen defined by the shaft 22′ and/or within a wall of theshaft 22′.

With reference to FIGS. 1A to 2, the medical positioning system 14 willnow be described in further detail. The medical positioning system 14can be provided for determining a position and/or orientation of theposition sensor 28 of the catheter 12, and thus, the position and/ororientation of the catheter 12. In some embodiments, the medicalpositioning system 14 may comprise a magnetic field-based system suchas, for example, the MediGuide™ system from MediGuide Ltd. (now owned bySt. Jude Medical, Inc.), and as generally shown with reference to one ormore of U.S. Pat. Nos. 6,233,476; 7,197,354; and 7,386,339, the entiredisclosures of which are incorporated herein by reference.

In some embodiments, and in general terms, the medical positioningsystem 14 comprises, at least in part, an apparatus 36 for generating amagnetic field for tracking of an object (e.g., catheter 12). Theapparatus 36 can be configured to generate low-strength magneticfield(s) in and around the patient's chest cavity in an area ofinterest, which can be defined as a three-dimensional space designatedas area of interest 38 in FIG. 2. In such an embodiment, and as brieflydescribed above, the catheter 12 includes a position sensor 28, which isa magnetic position sensor configured to detect one or morecharacteristics of the low-strength magnetic field(s) applied by theapparatus 36 when the position sensor 28 is disposed within the area ofinterest 38.

The position sensor 28, which in an exemplary embodiment comprises amagnetic coil (e.g., as discussed in relation to FIG. 1B), can beelectrically connected with a computer (e.g., processing core) andconfigured to generate a signal corresponding to the sensedcharacteristics of the magnetic field(s) to which the magnetic coil isexposed. The processing core can be responsive to the detected signaland can be configured to calculate a three-dimensional position and/ororientation reading for the position sensor 28. Thus, the medicalpositioning system 14 enables real-time tracking of each position sensor28 of the catheter 12 in three-dimensional space, and therefore,real-time tracking of the catheter 12.

The medical positioning system 14 can utilize software, hardware,firmware, and/or logic to perform a number of functions describedherein. The medical positioning system 14 can include a combination ofhardware and instructions to share information. The hardware, forexample can include a processing resource and/or a memory resource(e.g., non-transitory computer-readable medium (CRM) database, etc.). Aprocessing resource, as used herein, can include a number of processorscapable of executing instructions stored by the memory resource. Theprocessing resource can be integrated in a single device or distributedacross multiple devices. The instructions (e.g., computer-readableinstructions (CRI)) can include instructions stored on the memoryresource and executable by the processing resource for providing controlover a magnetic field and/or performing the method 220 discussed inrelation to FIG. 9, in an example

The medical positioning system 14 can utilize software, hardware,firmware, and/or logic to perform a number of functions. The medicalpositioning system 14 can include a number of remote computing devices.

The medical positioning system 14 can be a combination of hardware andprogram instructions configured to perform a number of functions. Thehardware, for example, can include one or more processing resources,computer readable medium (CRM), etc. The program instructions (e.g.,computer-readable instructions (CRI)) can include instructions stored onCRM and executable by the processing resource to implement a desiredfunction (e.g., determining an attenuation term for the second signal atthe second frequency based on the filtered first signal). The CRI canalso be stored in remote memory managed by a server and represent aninstallation package that can be downloaded, installed, and executed.The medical positioning system 14 can include memory resources, and theprocessing resources can be coupled to the memory resources. Theprocessing resources can execute CRI that can be stored on an internalor external non-transitory CRM. The processing resources can execute CRIto perform various functions, including the functions described herein,for example, with respect to FIG. 9.

In some embodiments, the apparatus 36 can be located underneath apatient examination table 46, between an x-ray source 40 and the patientexamination table 46. For example, the apparatus 36 can be connectedwith the patient examination table 46. In some embodiments, theapparatus 36 can be placed beneath the patient's body 16. For example,the apparatus 36 can be placed between the patient's body 16 and thepatient examination table 46 (e.g., beneath a mattress. In someembodiments, the apparatus 36 can be placed within the patientexamination table 46. In some embodiments, the apparatus 36 can be amobile device, which can be placed on a chest of the patient and used togenerate the magnetic field for tracking of the object.

In an example, challenges can be associated with generating a magneticfield for tracking an object, because the magnetic field can bedistorted as a result of objects that are located proximate to themagnetic field and/or a generator that produces the magnetic field. Forexample, magnetic field-distorting components can be located proximatelyto a magnetic field generator (e.g., apparatus 36) and can include thex-ray source 40, portions of the patient examination table 46, a c-arm42, and/or an x-ray image intensifier 44 associated with the medicalpositioning system 14. As such, the magnetic field-distorting componentscan have an effect on the magnetic field and cause distortions in themagnetic field. In some cases, even objects that are located far awayfrom the magnetic field generator and/or the magnetic field produced bythe magnetic field generator can cause distortions to the magneticfield. Part of the distortion can be to the magnetic field locatedwithin the area of interest 38. This can be problematic, because eachposition sensor 28 of the catheter 12 may benefit from a consistent(e.g., undistorted) magnetic field to determine a position and/ororientation of the position sensor 28 and/or catheter 12.

In an example, a source of the disturbance to the magnetic field can bean eddy current effect and/or a change in a magnetic permeability causedby magnetic field-distorting components. In an example, the magneticfield-distorting components can include conductive and/or magneticallypermeable objects located within a proximity to the apparatus 36 and/ora magnetic field produced by the apparatus 36. In some examples, wherethe magnetic field-distorting component is stationary, an eddy currentcaused by the magnetic field-distorting component can be factored outwhen determining a location of the catheter 12, in an example, throughcalibration. However, in a medical positioning system 14, such as thatdepicted in FIG. 2, magnetic field-distorting components (e.g., x-raysource 40, c-arm 42, x-ray image intensifier 44, patient examinationtable 46) can move with respect to the apparatus 36 and can causevarying disturbances to the magnetic field produced by the apparatus 36,which can be unpredictable.

In some examples, the x-ray source 40 and the x-ray image intensifier 44can be the greatest source of magnetic field distortion. Because themagnetic field-distorting components can move with respect to theapparatus 36, eddy currents produced by the magnetic field-distortingcomponents can constantly vary and can be difficult to factor out (e.g.,factor out a magnetic disturbance from a signal produced by a magneticposition sensor disposed in the magnetic field).

In some examples, the medical positioning system 14 can include animpedance-based system for determination of a position and/ororientation of the catheter 12. However, a distorted representation of ageometry of the heart can be generated when using an impedance-onlybased system, such as an Ensite™ system from St. Jude Medical, Inc. Forinstance, electrical currents used in an impedance based system cantravel three-dimensionally along a path of least resistivity. As such,part of the electrical currents can leave a transverse plane with bloodflow, for example, through an impedance transfer. Factoring in impedancetransfer can involve a non-linear solution, which can result in thedistorted representation of the geometry of the heart.

Accordingly, some embodiments of the present disclosure can reduceand/or eliminate distortions in the magnetic field produced by theapparatus 36 by reducing a strength of the magnetic field produced bythe apparatus 36 in a vicinity of the magnetic field-distortingcomponents. For example, the apparatus 36 can be moved within a closeproximity to the area of interest 38 that is closer than thoughtpossible. Thus, the magnetic field strength can be concentrated in thevolume of interest 38. Accordingly, there can be less distortion of themagnetic field caused by distant objects. This can result in a reductionin the shift and/or drift associated with coordinates determined throughthe impedance-based system, as a result of the reduction and/orelimination of distortion in the magnetic field.

For example, a magnetic field generator that produces a magnetic fieldof a lesser magnitude can be placed proximate to the area of interest38, such that a size of a magnetic field produced outside the area ofinterest 38 by the magnetic field generator is reduced, thus reducingchances for disturbance of the magnetic field by the magneticfield-distorting components.

Some embodiments of the present disclosure can lessen an effect thatmagnetic field-distorting components have on the magnetic field producedby the apparatus 36. For example, embodiments of the present disclosurecan generate magnetic fields of multiple frequencies. The multiplefrequencies can include a lower frequency and a higher frequency. Thelower frequency field can remain unperturbated when magnetic fielddisturbing object(s) move within a proximity to the lower frequencyfield. The lower frequency can be used to calibrate the higher frequencyin some embodiments to adjust for effects that the magneticfield-disturbing components have on the magnetic field of the higherfrequency.

Magnetic tracking systems can employ a type of magnetic field generatorthat includes an arrangement of electrically excited coils. In theMediguide™ system, this is referred to as a magnetic transmitter array(MTA). In previous systems, conventional coils (e.g., copper coils) cancause interference with a fluoroscopy image. For example, whenconventional coils are placed between the patient and the fluoroscopyimage beam and detector, the coils can appear on the fluoroscopy image,making it difficult to use the fluoroscopy image in catheter navigation.

Some embodiments of the present disclosure include an advantageousmagnetic field generator, as described in more detail below. In someembodiments, the magnetic field generator can be fluorolucent. In anexample, the magnetic field generator can be translucent in thefluoroscopy image and various instruments and/or anatomical features ofthe patient (e.g., heart) can be visible in the fluoroscopic image andare not obscured by the magnetic field generator in the fluoroscopicimage. Fluorolucent can be defined as being translucent in a fluoroscopyimage. For example, the fluorolucent magnetic field generator can bemore translucent in a fluoroscopy image than a non-fluorolucent magneticfield generator of a same thickness formed from copper. This can make iteasier for a physician to identify particular anatomical features and/orthe catheter in the fluoroscopy image.

FIG. 3A depicts a top view of a fluorolucent magnetic transmittingelement 50 prior to being folded, in accordance with embodiments of thepresent disclosure. Some embodiments of the present disclosure caninclude a fluorolucent magnetic transmitting element 50 for generating amagnetic field for tracking of an object. For example, with furtherreference to FIG. 2, a catheter 12 equipped with a position sensor 28can be placed within the area of interest 38 and the position sensor 28can generate a particular signal depending on where the position sensor28 is within the area of interest 38 (i.e., the magnetic field producedby the fluorolucent magnetic transmitting element 50).

To minimize an influence of magnetic field-distorting components (e.g.,c-arm movement), it can be desirable to move the fluorolucent magnetictransmitting element 50 (e.g., transmitter coils) as close as possibleto the navigational domain The magnitude of metallic interference is afunction of both the distances between the fluorolucent magnetictransmitting element 50 and position sensor 28 (e.g., coil) and betweenthe transmitting element and field-distorting component. Conventionaltransmitter coils (e.g., copper wound coils) can only be placed so closeto the navigational domain before the conventional transmitter coilsthemselves appear in the fluoroscopic image, obscuring clinicallyrelevant details and limiting the clinical utility of the primaryimaging modality. In an example, conventional transmitter coils may beplaced no closer than 30 centimeters of the navigational domain, beforethe conventional transmitter coils appear in the fluoroscopic image. Forinstance, the material (e.g., copper) from which the conventionaltransmitter coil is formed can begin to scatter X-ray photons andappears in the fluoroscopic image when the conventional transmitter coilis placed closer than 30 centimeters to the navigational domain.

In contrast, transmitter coils of the present disclosure can be planarand can be made thin enough to lie directly beneath a patient. Forexample, in some embodiments of the present disclosure, the fluorolucentmagnetic transmitting element 50 can be formed from a planar substrate.In an example, the fluorolucent magnetic transmitting element 50 caninclude planar coils that can be made thin enough to lie directlybeneath a patient. In some embodiments, the fluorolucent magnetictransmitting element 50 can be disposed between a mattress and table, asdescribed in U.S. application Ser. No. 15/034,474, which is herebyincorporated by reference as though fully set forth herein. In someembodiments, the fluorolucent magnetic transmitting element 50 can beplaced within 5 centimeters of the navigational domain

A maximum dimension of the fluorolucent magnetic transmitting element 50can be defined at an upper limit by a size of a patient examinationtable 46 and/or defined by a number of fluorolucent magnetictransmitting elements 50 that need to be placed in proximity to thenavigational domain (e.g., area of interest 38) in order to create anumber of different signals for receipt by the position sensor 28.

With reference to magnetic transmitting elements formed of copper (e.g.,copper magnetic transmitting element), an amount of energy that can bedissipated from the copper magnetic transmitting element in the form ofheat can be limited by a thickness of a mattress associated with thepatient examination table 46. For example, the patient examination table46 can include a frame and a mattress that has a multiplicity of layersor heavy layer weights associated with the mattress that act as aninsulator. The copper magnetic transmitting element can be disposedbetween the mattress and the frame. The mattress can insulate a patientfrom heat produced by the copper magnetic transmitting element and theheat produced by the copper magnetic transmitting element can bedissipated through the frame, which can act as a conductor. An amount ofcopper included in the copper magnetic transmitting element can beincreased, thus decreasing a resistance associated with the coppermagnetic transmitting element and decreasing an amount of heat generatedby the magnetic transmitting element as a current flows through thetransmitting element.

As a result of a standard thickness associated with a mattress, coppermagnetic transmitting elements can be made with enough copper that whilethe copper magnetic transmitting element produces an amount of heat thatcan be dissipated by the frame of the patient examination table 46 andinsulated from the patient by the mattress; the amount of copper withwhich the transmitting element is made causes it to be visible on afluoroscopy image, oftentimes obscuring the fluoroscopy image. Incontrast, embodiments of the present disclosure can provide afluorolucent magnetic transmitting element made with enough fluorolucentmaterial (e.g., aluminum), such that a standard thickness mattress caninsulate a patient from heat produced by the fluorolucent magnetictransmitting element, while the fluorolucent magnetic transmittingelement remains fluorolucent in the fluoroscopy image.

The fluorolucent magnetic transmitting element 50 can include a firstspiral trace 52 and a second spiral trace 54. In some embodiments, thespiral traces can be formed on a first spiral arm 51 and a second spiralarm 53. For example, the first spiral trace 52 can be formed on thefirst spiral arm 51 and the second spiral trace 54 can be formed on thesecond spiral arm 53. In some embodiments, the first spiral arm 51 andthe second spiral arm 53 can be formed from an insulative material(e.g., polyimide) and the first spiral trace 52 and the second spiraltrace 54 can be formed on a surface of the insulative material.

In some embodiments, as further discussed herein, the first spiral arm51 and the second spiral arm 53 can be formed from an insulativematerial and/or fluorolucent material (e.g., a polymer) and the firstspiral trace 52 and the second spiral trace 54 can be formed in aninterior of the first spiral arm 51 and the second spiral arm 53. Forexample, the first spiral arm 51 and the second spiral arm 53 can be acoating that surrounds the first spiral trace 52 and the second spiraltrace 54. In some embodiments, the first spiral trace 52 and the secondspiral trace 54 can be disposed on a polymer, such as a polyimide. Thefirst spiral trace 52 and the second spiral trace 54 can be sandwichedbetween the polyimide and an insulating epoxy solder mask to form thefirst spiral arm 51 and the second spiral arm 53. Alternatively, in someembodiments, the first spiral arm 51 and the second spiral arm 53 canact as the first spiral trace 52 and the second spiral trace 54,respectively. For example, the first spiral arm 51 and the second spiralarm 53 can be formed from a conductive fluorolucent material (e.g.,aluminum). As further discussed herein, when referring to the firstspiral trace 52 and the second spiral trace 54, this can include thefirst spiral arm 51 and the second spiral arm 53 when the first spiralarm 51 and the second spiral arm 53 are formed from a conductivefluorolucent material.

In embodiments of the present disclosure, a substrate such as aluminumis used to create the spiral traces 52, 54. Although aluminum hasapproximately 60 percent of the electrical conductivity of copper, ithas approximately 30 percent the density of copper and atomic nucleithat are lighter, resulting in fluorolucency of the fluorolucentmagnetic transmitting element 50 in a fluoroscopy image (e.g., a greatlyreduced x-ray footprint or visibility). The fluorolucency is attained atthicknesses of the fluorolucent magnetic transmitting element 50 thatyield comparable electrical resistance to a copper magnetic transmittingelement of the same size and/or thickness. In some embodiments of thepresent disclosure, the fluorolucent magnetic transmitting element 50can provide advantages when used in conjunction with magnetic resonanceimaging (MRI). For example, the fluorolucent magnetic transmittingelement 50 can be compatible with magnetic fields produced via MRI andcan be sized such that the fluorolucent magnetic transmitting element 50and/or an array of fluorolucent magnetic transmitting elements fitsinside of an MRI scanner tube, when in position under a patient.

In some embodiments of the present disclosure, a first spiral trace 52extends from a first outer origin 56 inward to a central origin 58. Thefirst spiral trace 52 can form one or more loops around the centralorigin 58 as it extends inward toward the central origin 58. As depictedin FIG. 3A, the first spiral trace 52 can form approximately two and ahalf loops around the central origin 58. However, more than two and ahalf loops or less than two and a half loops can be formed by the firstspiral trace 52 around the central origin 58 in some embodiments. Insome embodiments, the first spiral trace 52 can extend from the firstouter origin 56 to the central origin 58 in a first direction. Forexample, as depicted, the first spiral trace 52 can extend from thefirst outer origin 56 to the central origin 58 in a counter-clockwisedirection.

In some embodiments, the second spiral trace 54 can extend from thecentral origin 58 outward to a second outer origin 60. The second spiraltrace 54 extends from the central origin 58 to the second outer origin60 in a second direction that is opposite of the first direction. Insome embodiments, the fluorolucent magnetic transmitting element 50 canbe formed from a planar piece of material (e.g., fluorolucent material).The planar piece of material can be cut between the first spiral trace52 and the second spiral trace 54 to the central origin 58. For example,a first cut 62 and a second cut 64 can be formed in the fluorolucentmagnetic transmitting element 50 between the first spiral trace 52 andthe second spiral trace 54. The first cut 62 can be formed between thefirst outer origin 56 and the second spiral trace 54, in someembodiments. For example, the first cut 62 can originate from a firstorigination point 66 and can terminate at a first termination point 68.The second cut 64 can be formed between the second outer origin 60 andthe first spiral trace 52, in some embodiments. For example, the secondcut 64 can originate from a second origination point 70 and canterminate at a second termination point 72.

In some embodiments, an amount of material can be left at the centralorigin so the first spiral trace 52 and the second spiral trace 54remain connected at the central origin 58. For example, material can beleft between the first termination point 68 of the first cut 62 and thesecond termination point 72 of the second cut 64. As such, the firstspiral trace 52 and the second spiral trace 54 can be formed from acontinuous piece of material and no joints can exist between the firstspiral trace 52 and the second spiral trace 54. In an example, no jointsexists between a first inner origin 74 of the first spiral trace 52 anda second inner origin 76 of the second spiral trace 54. For instance, aconnection can be formed between the first inner origin 74 and thesecond inner origin 76 by a continuous trace of material. As such,embodiments of the present disclosure can avoid joining the circuitelements (e.g., first spiral trace 52, second spiral trace 54) at thefirst inner origin 74 and the second inner origin 76 by soldering,welding, wire-bonding, electroplating through-holes, vias, etc.

In some embodiments, the fluorolucent magnetic transmitting element 50can be formed via a forging, casting, cutting, machining, or otherprocess. For example, the fluorolucent magnetic transmitting element 50can be formed such that slits are defined between the first spiral trace52 and the second spiral trace 54. The fluorolucent magnetictransmitting element 50 can be formed from a sheet of aluminum, in someembodiments. Alternatively, the fluorolucent magnetic transmittingelement 50 can be formed from substrates other than aluminum. In someembodiments, the fluorolucent magnetic transmitting element 50 can beformed from another type of fluorolucent material. In an example, thefluorolucent magnetic transmitting element 50 can be formed from afluorolucent material such as silver printed ink or carbon graphene.

While some embodiments of the present disclosure can form thefluorolucent magnetic transmitting element 50 via subtractive methods,such as cutting, machining, etc., additive type methods can also be usedfor form the fluorolucent magnetic transmitting element 50, such asdepositing of fluorolucent material in a particular patter viadeposition, printing, etc. In some embodiments, the fluorolucentmagnetic transmitting element 50 can be printed with silver printed ink,for example, with a three-dimensional printer. Alternatively, in someembodiments, a planar layer of carbon graphene can be cut to form thefirst spiral trace 52 and the second spiral trace 54. In someembodiments, one or more layers of carbon graphene can be laid to formthe spiral trace 52 and the second spiral trace 54. As such, the firstspiral trace 52 and the second spiral trace 54 can be formed withoutcutting.

FIG. 3B depicts an isometric side view of the fluorolucent magnetictransmitting element in FIG. 3A partially folded, in accordance withembodiments of the present disclosure. In some embodiments, thefluorolucent magnetic transmitting element 50-1 can be folded across anaxis defined by line aa at the central origin. The axis aa can extendacross the fluorolucent magnetic transmitting element 50-1, such thatthe axis aa divides the fluorolucent magnetic transmitting element 50-1in half and the first outer origin 56 and the second outer origin 60 arediametrically opposed to one another. For example, as depicted in FIG.3B, the fluorolucent magnetic transmitting element 50-1 is folded acrossthe axis aa at the central origin 58-1.

The continuous piece of material that forms the first spiral trace 52-1and the second spiral trace 54-1 and that also forms the first spiralarm 51-1 and the second spiral arm 53-1 can be folded at the centralorigin 58-1. As depicted, the first spiral trace 52-1 and the secondspiral trace 54-1 are being folded along the axis aa at the centralorigin 58-1. In an example, the fluorolucent magnetic transmittingelement 50-1 can be folded at the central origin 58-1, such that acrease only occurs at the central origin 58-1 along axis aa. In someembodiments care must be taken to prevent the fluorolucent magnetictransmitting element from breaking along the crease. For example, amandrel can be used when forming the crease at the central origin 58-1along axis aa. The fluorolucent magnetic transmitting element 50-1 canbe folded at the central origin 58-1 such that the first spiral trace52-1 is rotated 180 degrees about the axis aa, alternatively, the secondspiral trace 54-1 can be rotated 180 degrees about the axis aa. In anexample, upon folding the fluorolucent magnetic transmitting element50-1, portions of each spiral trace 52-1, 54-1 not located at thecentral origin 58-1 along axis aa may not be creased.

FIG. 3C depicts a top view of the fluorolucent magnetic transmittingelement 50-2 in FIG. 3A after folding, in accordance with embodiments ofthe present disclosure. For purposes of illustration, the fluorolucentmagnetic transmitting element 50-2 is depicted on a background 79 tohelp demonstrate the fluorolucent magnetic transmitting element 50-2. Insome embodiments, when the fluorolucent magnetic transmitting element50-2, as depicted in FIG. 3A, is folded along the axis aa at the centralorigin 58-2, the first spiral trace 52-2 can overlap with (e.g., bestacked on top of) an area of the second spiral trace 54-2. For example,the first spiral trace 52-2 can overlap the second spiral trace 54-4 atoverlapping area 81. Although overlapping area 81 is discussed herein,multiple portions of the first spiral trace 52-2 and the second spiraltrace 54-4 can overlap, as depicted. As used with respect to FIGS. 3A,3B, and 3C, the fluorolucent magnetic transmitting element 50 is in anunfolded state, the fluorolucent magnetic transmitting element 50-1 isin a partially folded state, and the fluorolucent magnetic transmittingelement 50-2 is in a folded state.

In some embodiments, the first spiral trace 52-2 and/or the secondspiral trace 54-2 can be rotated (e.g., 180 degrees) about the axis aa,such that a crease is formed between the first spiral trace 52-2 and thesecond spiral trace 54-2 along the axis aa. For example, the firstspiral trace 52-2 can overlap the second spiral trace 54-2 on a firstside 80 of the axis aa and the second spiral trace 54-2 can overlap thefirst spiral trace 52-2 on a second side 82 of the axis aa. In someembodiments, a first electrical terminal (also referred to herein asfirst outer origin) can be disposed at a first outer origin 56-2 of thefirst spiral trace 52-2 and a second electrical terminal (also referredto herein as second outer origin) can be disposed at a second outerorigin 60-2 of the second spiral trace 54-2.

In some embodiments, a current can be supplied to the first electricalterminal or the second electrical terminal and the current can flowthrough the fluorolucent magnetic transmitting element 50-2. If currentis supplied to the first electrical terminal at the first outer origin56-2, the current can flow clockwise, as depicted by the arrows in FIG.3C, along the first spiral trace 52-2 toward the central origin 58-2 andthen the current can flow from the central origin 58-2 along the secondspiral trace 54-2, also in a clockwise direction, as further depicted bythe arrows in FIG. 3C, toward the second outer origin 60-2 and thesecond electrical terminal at the second outer origin 60-2. As such, thecurrent can flow through the fluorolucent magnetic transmitting element50-2 from the first electrical terminal to the second electricalterminal in a clockwise direction and can produce a magnetic field.

Alternatively, current can be supplied to the second electrical terminalat the second outer origin 60-2. The current can flow counter-clockwisealong the second spiral trace 54-2 toward the central origin 58-2 andthen the current can flow from the central origin 58-2 along the firstspiral trace 52-2, also in a counter-clockwise direction toward thefirst outer origin 56-2 and the second electrical terminal at the firstouter origin 56-2. As such, the current can flow through thefluorolucent magnetic transmitting element 50-2 from the firstelectrical terminal to the second electrical terminal in acounter-clockwise direction and can produce a magnetic field.

Although the description of FIG. 3C references a fluorolucent magnetictransmitting element, the configuration can be beneficial for anon-fluorolucent magnetic transmitting element (e.g., a magnetictransmitting element formed of a non-fluorolucent material such ascopper), as well. In an example, a uniform current direction ismaintained by the configuration depicted in FIG. 3C, while theelectrical terminals (e.g., first outer origin 56-2 and second outerorigin 60-2) are located at an outer portion of the transmittingelement. Some transmitting elements can maintain a uniform currentdirection, however, one electrical terminal is located on an outside ofthe transmitting element and one electrical terminal can be located at acentral origin of the transmitting element, thus making electricalconnection of the transmitting element more difficult. Embodiments ofthe present disclosure can avoid this difficulty. However, someembodiments, of the present disclosure can include a magnetictransmitting element that is formed of a fluorolucent material thatincludes one electrical terminal located on an outside of thetransmitting element. A trace of the magnetic transmitting element canbe coiled inward from the electrical terminal located on the outside ofthe transmitting element towards a central origin and can terminate atan inner terminal.

Some embodiments of the present disclosure can include a magnetictransmitting assembly as discussed in relation to U.S. application Ser.No. 15/034,474, which is hereby incorporated by reference as thoughfully set forth herein, that is made from a fluorolucent material (e.g.,aluminum).

FIG. 3D depicts overlapping area 81′ that includes a first spiral trace52-2′ and a second spiral trace 54-2′ and an insulating material 55disposed between the first spiral trace 52-2′ and the second spiraltrace 54-2′. For example, an insulating material can be disposed betweenthe overlapping area 81′ of the first spiral trace 52-2′ and the secondspiral trace 54-2′. In some embodiments, the insulating material canprevent the first spiral trace 52-2′ and the second spiral trace 54-2′contacting one another, causing a disturbance to the flow of current. Inan example, the insulating material can prevent a short from occurringwhere the first spiral trace 52-2′ and the second spiral trace 54-2′overlap, allowing for the current to flow completely through the firstspiral trace 52-2′ and the second spiral trace 54-2′.

In some embodiments, although not depicted, each spiral trace 52-2′,54-2′ can be coated in an insulated material. For example, a top,bottom, and opposing lateral sides of each spiral trace 52-2′, 54-2′ canbe coated in an insulated material. Accordingly, as the first spiraltrace 52-2′ and second spiral trace 54-2′ are creased at their centralorigin and the first spiral trace 52-2′ and the second spiral trace54-2′ overlap one another, the first spiral trace 52-2′ and the secondspiral trace 54-2′ can remain electrically isolated from one in theoverlapping area 81′, due to the insulative coating on each of the firstspiral trace 52-2′ and the second spiral trace 54-2′ being disposedbetween the traces.

With further reference to FIG. 3C, in an example, a magnetic field canbe generated by the fluorolucent magnetic transmitting element 50-2. Thecurrent can flow through the fluorolucent magnetic transmitting element50-2 in a uniform direction from the first electrical terminal to thesecond electrical terminal or from the second electrical terminal to thefirst electrical terminal, as previously discussed herein. For example,the current can flow in a uniform direction, as indicated by the arrowsdepicted in FIG. 3C.

Although the fluorolucent magnetic transmitting element 50-2 is depictedas generally circular in shape, the fluorolucent magnetic transmittingelement 50-2 can be square, rectangular, triangular, polygonal, oval,elliptical, etc. In an example, the maximum dimension of thefluorolucent magnetic transmitting element 50-2 can be defined by thecircle 78 that is depicted in phantom in FIG. 3C. In an example, thecircle 78 can have a diameter in a range from 6 to 14 centimeters.However, the diameter of the circle 78 can be greater than 14centimeters and less than 6 centimeters in some embodiments. Regardlessof whether the fluorolucent magnetic transmitting element 50-2 issquare, rectangular, triangular, polygonal, etc., the magnetictransmitting element 50-2 magnetic transmitting element can have amaximum dimension such that it fits within the circle 78, in someembodiments. For purposes of illustration and to distinguish the circle78 from the fluorolucent magnetic transmitting element 50-2, the circle78 is depicted as having a larger diameter than the fluorolucentmagnetic transmitting element. Embodiments of the present disclosure caninclude a fluorolucent magnetic transmitting element with a maximumdimension that is the same as a diameter of the circle 78.

The continuous piece of substrate that forms the fluorolucent magnetictransmitting element 50-2 allows for the current to continuously passthrough the fluorolucent magnetic transmitting element 50-2 without theuse of any joints. Some prior approaches have employed processes tomanufacture planar magnetic transmitters using printed circuit boardprocesses. A number of vias can be produced between segments of printedcircuit board to form spiral traces and to join multiple spiral tracestogether, such that current can continuously flow through the spiraltraces. Due to a greater reactivity of aluminum, electroplating vias canbe ineffective when the substrate or a portion of the substrate isformed from aluminum.

Embodiments of the present disclosure can allow for a first spiral trace52-2 and a second spiral trace 54-2 to be formed from a unitary piece ofmaterial, as discussed herein, while providing a fluorolucent magnetictransmitting element 50-2 that can provide for a unidirectional currentflow. For example, folding the first spiral arm 51-2 (e.g., first spiraltrace 52-2) and the second spiral arm 53-2 (e.g., second spiral trace54-2) of the fluorolucent magnetic transmitting element 50-2 at thecentral origin 58-2 can allow for the first spiral arm 51-2 (e.g., firstspiral trace 52-2) and the second spiral arm 53-2 (e.g., second spiraltrace 54-2) to be formed from a unitary piece of material. Thus,embodiments of the present disclosure can avoid use of vias or othertypes of connectors to join segments and multiple spiral tracestogether. For example, embodiments of the present disclosure can utilizea single piece of material (e.g., aluminum) to form the magnetictransmitting element. While a first spiral trace 52-2 and a secondspiral trace 54-2 are discussed as two traces, the first and secondtraces 52-2, 54-2 are formed from a unitary piece of material, thusavoiding the use of vias.

FIG. 4A depicts a top view of a magnetic transmitting array 90 thatincludes a set of magnetic transmitting elements 92-1, 92-2, 92-3, 92-4,94-1, 94-2, 94-3, 94-4, 96-1, 96-2, 96-3, 96-4, 98-1, 98-2, 98-3, and98-4, in accordance with embodiments of the present disclosure. Someembodiments of the present disclosure can prevent neighboring magneticdrive coils from coupling with each other. In an example, multiple drivecoils can be used to provide sufficient spatially-unique andorientation-unique signaling at any point in 3D space where it isdesired to determine the location and orientation of a position sensor28 (e.g., magnetic sensing coil). The unique signals can be createdusing a specific frequency to excite each magnetic drive coil, althoughtime domain methods could also be employed. A sense coil amplifier andsignal processor then measure a unique amplitude value attributable toeach drive coil (in the case of frequency division multiplexing,synchronous demodulation for example is used). It is important thatexcitation from one drive coil does not couple into adjacent drivecoils, and then radiate from those coils, as this can confound thesubsequent means to derive accurate location of the magnetic sensingcoil. Assuming each coil is excited by a unique frequency, the desiredphysical behavior which leads to the simplest mathematical model is thateach frequency only represents emanation from a single drive coil at itslocation. Coupling and re-radiating a signal (e.g., excitation signal)from neighboring coils is undesirable, as this can confound themathematical model.

To locate and orient a magnetic position sensor 28 (e.g., magneticsensing coil), 3 degrees of freedom (e.g., x, y, z) for the location canbe desired and 2 degrees of freedom (e.g., pitch and yaw) for theorientation. This means that a minimum of 5 drive coils may be required.In some embodiments, more coils can be useful for solving for additionalparameters such as system gain, or for extending the viable sensingregion. In some embodiments, coils with a low inductance may besusceptible to coupling with neighboring coils and re-radiating thesignal from neighboring coils. Embodiments of the present disclosure canreduce and/or eliminate coupling between neighboring coils. In someembodiments of the present disclosure, the fluorolucent magnetictransmitting element, as discussed in relation to FIG. 3C, can includeone layer of substrate, for example, when the magnetic transmittingelement is made from aluminum. To increase a number of layers, themagnetic transmitting array 90 can include a number of fluorolucentmagnetic transmitting elements arranged in multiple layers. Thefluorolucent magnetic transmitting elements can be those, as discussedin relation to FIG. 3C. Alternatively, or in addition, the magnetictransmitting array 90 can include magnetic transmitting elements, suchas those discussed in relation to U.S. application Ser. No. 15/034,474,which is hereby incorporated by reference as though fully set forthherein. For example, the magnetic transmitting array 90 can include afirst layer of magnetic transmitting elements, similar to thosediscussed in relation to FIG. 3. The first layer of magnetictransmitting elements can, for example, include a first magnetictransmitting element 92-1, a second magnetic transmitting element 92-2,a third magnetic transmitting element 92-3, a fourth magnetictransmitting element 92-4.

In some embodiments, each first layer magnetic transmitting element92-1, 92-2, 92-3, 92-4 does not overlap one another. For example, eachfirst layer magnetic transmitting element 92-1, 92-2, 92-3, 92-4 can bespaced apart from neighboring magnetic transmitting elements of the samelayer. In some embodiments, the first layer magnetic transmittingelements 92-1, 92-2, 92-3, 92-4 can abut neighboring magnetictransmitting elements in the same layer. For example, the first magnetictransmitting element 92-1 of the first layer can abut the third magnetictransmitting element 92-3 of the first layer, but can be spaced apartfrom the second magnetic transmitting element 92-2 of the first layer.In some embodiments, the first layer magnetic transmitting elements92-1, 92-2, 92-3, 92-4 can be arranged in a grid fashion, such that thecentral origin (e.g., central origins 93-1, 93-2, 93-3, 93-4) of each ofthe first layer magnetic transmitting elements 92-1, 92-2, 92-3, 92-4forms a corner of a square, rectangle, rhombus, parallelogram, etc.

Further, the magnetic transmitting array 90 can include a second layerof magnetic transmitting elements 94-1, 94-2, 94-3, 94-4, a third layerof magnetic transmitting elements 96-1, 96-2, 96-3, 96-4, and a fourthlayer of magnetic transmitting elements 98-1, 98-2, 98-3, 98-4. Asdiscussed, the first layer, second layer, third layer, and fourth layermagnetic transmitting elements can be fluorolucent magnetic transmittingelements, such as those discussed with respect to FIG. 3C. The magnetictransmitting elements in the second layer, third layer, and/or fourthlayer can be arranged in a spatial relationship similar to thatdiscussed in relation to how the first layer magnetic transmittingelements 92-1, 92-2, 92-3, 92-4 are arranged, as described herein.

In some embodiments (not shown), the magnetic transmitting elements inthe second layer, third layer, and/or fourth layer can be arranged in adifferent spatial relationship than the first layer magnetictransmitting elements 92-1, 92-2, 92-3, 92-4. For example, the firstlayer magnetic transmitting elements 92-1, 92-2, 92-3, 92-4 can bearranged such that one or more other layers (e.g., second layer, thirdlayer, fourth layer) are arranged in a spatial relationship that isdifferent than the first layer magnetic transmitting elements 92-1,92-2, 92-3, 92-4. For example, the second layer magnetic transmittingelements 94-1, 94-2, 94-3, 94-4 can be arranged such that the centralorigin of each of the second layer magnetic transmitting elements 94-1,94-2, 94-3, 94-4 forms a corner of a rectangle, while the first layermagnetic transmitting elements 92-1, 92-2, 92-3, 92-4 are arranged suchthat the central origin of each of the first layer magnetic transmittingelements 92-1, 92-2, 92-3, 92-4 forms a corner of a square. Thus, eachof the first, second, third, and fourth layers of magnetic transmittingelements can be arranged in the same spatial relationship as the firstlayer magnetic transmitting elements 92-1, 92-2, 92-3, 92-4 or in adifferent spatial relationship than the first layer magnetictransmitting elements 92-1, 92-2, 92-3, 92-4.

Although four magnetic transmitting elements are depicted in each layerof the magnetic transmitting array 90, more than four magnetictransmitting elements or fewer than four magnetic transmitting elementscan be included in each layer of the magnetic transmitting array 90. Insome embodiments, magnetic transmitting elements in a range of from 1 to20 can be included in each layer of the magnetic transmitting array 90.In some embodiments, the number of magnetic transmitting elementsincluded in each respective layer of the magnetic transmitting array 90can be in a range from 2 to 15. In some embodiments, the number ofmagnetic transmitting elements included in each respective layer of themagnetic transmitting array 90 can be in a range from 3 to 10. In someembodiments, the number of magnetic transmitting elements included ineach respective layer of the magnetic transmitting array 90 can be in arange from 4 to 7. Further, although four layers of magnetictransmitting elements are depicted in the magnetic transmitting array90, more than four layers of magnetic transmitting elements or fewerthan four layers of magnetic transmitting elements can be included inthe magnetic transmitting array 90. Some embodiments of the presentdisclosure can include from 1 to 8 layers of magnetic transmittingelements in the magnetic transmitting array 90. Some embodiments of thepresent disclosure can include from 2 to 5 layers of magnetictransmitting elements in the magnetic transmitting array 90.

In some embodiments, each magnetic transmitting element in the second,third, and fourth layer do not overlap magnetic transmitting elementswithin each respective layer, similar to first layer magnetictransmitting elements 92-1, 92-2, 92-3, 92-4. For example, the secondlayer magnetic transmitting elements 94-1, 94-2, 94-3, 94-4 do notoverlap one another, nor do the magnetic transmitting elements in thethird layer and fourth layer overlap one another. In some embodiments,magnetic transmitting elements in each respective layer do not overlapto prevent a short from occurring between each magnetic transmittingelement in the layer.

In some embodiments, the first layer, second layer, third layer, andfourth layer magnetic transmitting elements can overlap magnetictransmitting elements in other layers. For example, as depicted, thesecond layer magnetic transmitting elements 94-1, 94-2, 94-3, 94-4 canoverlap (e.g., partially overlap) the first layer magnetic transmittingelements 92-1, 92-2, 92-3, 92-4; the third layer magnetic transmittingelements 96-1, 96-2, 96-3, 96-4 can overlap the first layer magnetictransmitting elements 92-1, 92-2, 92-3, 92-4 and the second layermagnetic transmitting elements 94-1, 94-2, 94-3, 94-4; and the fourthlayer magnetic transmitting elements 98-1, 98-2, 98-3, 98-4 can overlapthe first layer magnetic transmitting elements 92-1, 92-2, 92-3, 92-4;the second layer magnetic transmitting elements 94-1, 94-2, 94-3, 94-4;and the third layer magnetic transmitting elements 96-1, 96-2, 96-3,96-4.

Regardless of whether the magnetic transmitting element layers overlap,the layers may be arranged such that the magnetic transmitting elementsare organized in a hexagonal lattice pattern or structure when viewedfrom a direction perpendicular to a plane in which the elements of alayer lie (as illustrated in FIGS. 4A and 4C). In such embodiments, thecentral origins of the transmitting elements can be considered to alignwith the vertices of the lattice. In embodiments where there is overlapbetween magnetic transmitting elements in different layers, the relativeplacement of the magnetic transmitting elements between layers may beoptimized such that they are spread as much as possible within aconstrained area (e.g., to concentrate a magnetic field in a volumetricarea of interest such as a patient's body or, more specifically, thearea around and/or in a patient's heart, for example), while at the sametime minimizing the amount of obstruction produced in a fluoroscopicimage where X-rays are passing through the magnetic transmitting elementlayers. In such embodiments, the hexagonal lattice structure can beanalogized to a “beehive” like structure with overlapping “cells” asshown in FIG. 4A. As seen there, the radius of a transmitting elementmay be calculated as the square root of 3 divided by 2 times thedistance between vertices on the lattice (in other words, the radius ofa transmitting element may be equal to the “height” of an equilateraltriangle formed by three adjacent vertices on the lattice).

In more detail and with continued attention to FIG. 4A, the second layerof magnetic transmitting elements 94-1, 94-2, 94-3, 94-4 can be arrangedin a same spatial relationship as the first layer magnetic transmittingelements 92-1, 92-2, 92-3, 92-4 and the central origins (e.g., centralorigins 95-1, 95-2, 95-3, 95-4) of each of the second layer magnetictransmitting elements 94-1, 94-2, 94-3, 94-4 can be shifted in a firstdirection from the central origins (e.g., central origins 93-1, 93-2,93-3, 93-4) of the first layer magnetic transmitting elements 92-1,92-2, 92-3, 92-4. For example, as depicted, the central origins of eachof the second layer magnetic transmitting elements 94-1, 94-2, 94-3,94-4 can be shifted laterally in the first direction (e.g., to theright, with respect to the page) from the central origins of the firstlayer magnetic transmitting elements 92-1, 92-2, 92-3, 92-4.

In some embodiments, the third layer magnetic transmitting elements96-1, 96-2, 96-3, 96-4 can be shifted laterally and vertically withrespect to the first layer magnetic transmitting elements 92-1, 92-2,92-3, 92-4. As depicted, the central origins (e.g., central origins97-1, 97-2, 97-3, 97-4) of the third layer magnetic transmittingelements 96-1, 96-2, 96-3, 96-4 can be shifted between the centralorigins of the first layer magnetic transmitting elements 92-1, 92-2,92-3, 92-4 and the second layer magnetic transmitting elements 94-1,94-2, 94-3, 94-4. In an example, the central origins of the third layermagnetic transmitting elements 96-1, 96-2, 96-3, 96-4 can be shifted tothe right (with respect to the page) of the central origins of the firstlayer magnetic transmitting elements 92-1, 92-2, 92-3, 92-4 by a smalleramount than the central origins of the second layer magnetictransmitting elements 94-1, 94-2, 94-3, 94-4.

In addition the central origins of the third layer magnetic transmittingelements 96-1, 96-2, 96-3, 96-4 can be shifted vertically (e.g., upward)with respect to the central origins of the first layer magnetictransmitting elements 92-1, 92-2, 92-3, 92-4. In some embodiments, thefourth layer magnetic transmitting elements 98-1, 98-2, 98-3, 98-4 canbe shifted laterally with respect to the central origins of the firstlayer magnetic transmitting elements 92-1, 92-2, 92-3, 92-4, secondlayer magnetic transmitting elements 94-1, 94-2, 94-3, 94-4, and thirdlayer magnetic transmitting elements 96-1, 96-2, 96-3, 96-4. Forexample, the central origins of the fourth layer magnetic transmittingelements 98-1, 98-2, 98-3, 98-4 can be shifted to the right of thecentral origins of the first layer, second layer, and third layermagnetic transmitting elements.

In addition, the central origins of the fourth layer magnetictransmitting elements 98-1, 98-2, 98-3, 98-4 can be shifted vertically(e.g., upward) from the central origins of the first layer magnetictransmitting elements 92-1, 92-2, 92-3, 92-4. For example, the centralorigins (e.g., central origins 99-1, 99-2, 99-3, 99-4) of the fourthlayer magnetic transmitting elements 98-1, 98-2, 98-3, 98-4 can beshifted vertically from the first layer magnetic transmitting elements92-1, 92-2, 92-3, 92-4 a same amount as the origins of the third layermagnetic transmitting elements 96-1, 96-2, 96-3, 96-4. As such, theoverlapping magnetic transmitting elements can be arranged such that nothrough holes exist between the magnetic transmitting array 90, asdepicted in FIG. 4A. For example, as depicted, the third layer magnetictransmitting element 96-3 covers a through hole that would exist betweenthe first layer magnetic transmitting elements 92-1, 92-3 and secondlayer magnetic transmitting elements 94-1, 94-3.

To compensate for a low number of layers (e.g., two layers) of substrateforming the magnetic transmitting elements, the magnetic transmittingarray 90 of the present disclosure can include layers of magnetictransmitting elements (e.g., as discussed in relation to FIG. 3) thatoverlap one another. For example, the first layer is overlapped by thesecond layer, which is overlapped by the third layer, which isoverlapped by the fourth layer. A spacing between central origins ofeach magnetic transmitting element between neighboring layers can beapproximately a radius between each coil. A separation between thecentral origins can be required so that a condition of the inversesolution to determine coil location is well determined. For example, thecentral origins of the first layer magnetic transmitting elements 92-1,92-2, 92-3, 92-4 (e.g., central origins 93-1, 93-2, 93-3, 93-4) andadjacent second layer magnetic transmitting elements 94-1, 94-2, 94-3,94-4 (e.g., central origins 95-1, 95-2, 95-3, 95-4) can be separated bya distance equivalent to a radius of one of the magnetic transmittingelements in the magnetic transmitting array 90. For instance, the firstlayer magnetic transmitting element 92-1 can be separated fromneighboring second layer magnetic transmitting element 94-1 by adistance equivalent to a radius of one of the magnetic transmittingelements.

In some embodiments, the spacing between central origins of eachmagnetic transmitting element between neighboring layers can be greaterthan the radius between each coil. In some embodiments, the spacingbetween central origins of each magnetic transmitting element betweenneighboring layers can be less than the radius between each coil tocreate a more dense magnetic field.

As discussed herein, a central origin to central origin spacing ofneighboring magnetic transmitting elements can be equivalent to orgreater than a radius of one of the magnetic transmitting elements.Compared to a square array of square magnetic transmitting elements thatdoes not overlap and that is of the same characteristic size, eachmagnetic transmitting element can enclose 40 percent more area, whichwhen etched into an 11 centimeter diameter spiral with 1.8 mm pitchresults in 95 percent more field per layer at the same current used in asquare array of magnetic transmitting elements.

For the same dimensions, the trace length associated with the larger,overlapped spirals is only 10 percent longer than a trace length for asquare shaped coil. For a given field strength, the result is that thelarger overlapped spirals dissipate less than 30 percent of the heatcompared to the square array of magnetic transmitting elements. Giventhe ability to use much thicker aluminum layers than copper withoutobscuring the fluoroscopic image, the resistance per layer can bereduced accordingly, resulting in an x-ray transparent transmitter arraythat is approximately an order of magnitude more efficient at generatingan AC magnetic field than the square array of prior approaches.

As previously discussed, the overlapping magnetic transmitting elementscan be arranged such that no through holes exist between the magnetictransmitting array 90, as depicted in FIG. 4A. For example, as depicted,the third layer magnetic transmitting element 96-3 covers a through holethat would exist between the first layer magnetic transmitting elements92-1, 92-3 and second layer magnetic transmitting elements 94-1, 94-3.This can create a more dense magnetic field in some embodiments.

In some embodiments, the magnetic transmitting array 90 can be afluorolucent magnetic transmitting array 90. For example, fluorolucentmagnetic transmitting elements, such as those discussed in relation toFIG. 3C, can be included in the array 90. This can allow for themagnetic transmitting array 90 to be placed in a fluoro window 91, whichcan be a window through which x-rays from a fluoroscope pass. Thefluorolucent nature of the magnetic transmitting array 90 can allow forx-rays to pass through the fluoro window 91 and the array 90, thusproviding a fluoroscopic image that is unobstructed by the magnetictransmitting array 90.

FIG. 4B depicts a side view of an insulation layer 100 disposed betweena first layer of magnetic transmitting elements and a second layer oftransmitting elements, in accordance with embodiments of the presentdisclosure. In some embodiments an insulative layer can be disposedbetween one or more layers of the magnetic transmitting elements toprevent the magnetic transmitting elements from contacting one another.As depicted, the insulative layer 100 is disposed between first layermagnetic transmitting elements 92-3, 92-4 and second layer magnetictransmitting elements 94-3, 94-4. The insulative layer 100 can bedisposed between the first layer magnetic transmitting elements 92-1,92-2, 92-3, 92-4 and the second layer transmitting elements 94-1, 94-2,94-3, 94-4; between the second layer magnetic transmitting elements94-1, 94-2, 94-3, 94-4 and the third layer transmitting elements 96-1,96-2, 96-3, 96-4; and/or between the third layer magnetic transmittingelements 96-1, 96-2, 96-3, 96-4 and the fourth layer transmittingelements 98-1, 98-2, 98-3, 98-4.

FIG. 4C depicts a top view of a first layer of magnetic transmittingelements 102-1, 102-2, . . . , 102-16 of a magnetic transmitting array,in accordance with embodiments of the present disclosure. The magnetictransmitting elements 102-1, 102-2, . . . , 102-16 can be fluorolucent,in some embodiments, such as the fluorolucent magnetic transmittingelement discussed in relation to FIG. 3C. In an example, the first layermagnetic transmitting elements 102-1, 102-2, . . . , 102-16 can bearranged in a manner similar to how the first layer magnetictransmitting elements 92-1, 92-2, 92-3, 92-4 are arranged in FIG. 4A.For example, the first layer magnetic transmitting elements 102-1,102-2, . . . , 102-16 can be arranged in a first plane, forming a firstmagnetic assembly layer. The first layer magnetic transmitting elements102-1, 102-2, . . . , 102-16 do not overlap one another on the firstplane, as depicted in FIG. 4C.

In some embodiments, a connection lead tree 103 can electrically coupleeach one of the first layer magnetic transmitting elements 102-1, 102-2,. . . , 102-16 to a connection pad 104, via individual connection leads(e.g., connection lead 105). The connection pad 104 can be connected toa plurality of connection leads, each of which is electrically coupledwith one of the first layer magnetic transmitting elements 102-1, 102-2,. . . , 102-16. With reference to connection lead 105, the connectionlead 105 electrically couples the first layer magnetic transmittingelement 102-1 to the connection pad 104. Each of the magnetictransmitting elements 102-1, 102-2, . . . , 102-16 can be electricallycoupled to the connection pad via terminals located at an outer edge ofthe magnetic transmitting element, as depicted in FIG. 4C and previouslydiscussed in relation to FIG. 3C.

In some embodiments, the first layer magnetic transmitting elements102-1, 102-2, . . . , 102-16, the lead tree 103, and/or the connectionleads can be disposed on a substrate 101. In an example, the substratecan be rigid and/or flexible. In some embodiments, the substrate can bea printed circuit board on which the first layer magnetic transmittingelements 102-1, 102-2, . . . , 102-16 are disposed. In some embodiments,multiple layers of magnetic transmitting elements can be stacked on topof one another, as further described in relation to FIG. 4A. Forexample, one or more other layers of magnetic transmitting elements canbe stacked on top of the first layer magnetic transmitting elements102-1, 102-2, . . . , 102-16 and can be longitudinally or laterallyoffset from the first layer magnetic transmitting elements, as depictedand discussed in relation to FIG. 4A. In some embodiments, between 2 and10 layers of magnetic transmitting elements can be stacked on top of oneanother. In some embodiments, by stacking multiple layers of magnetictransmitting elements on top of one another, a lateral width of themagnetic transmitting array can be reduced, enabling the magnetictransmitting array to fit within a fluoro window. However, in someembodiments, a single layer of magnetic transmitting elements can beused in the magnetic transmitting array.

FIG. 5A depicts a diagrammatic a top view of a second embodiment of amagnetic transmitting assembly 106, in accordance with embodiments ofthe present disclosure. In some embodiments, the magnetic transmittingassembly 106 can include a frame 108 to which a plurality ofelectromagnetic transmitting elements 110-1, 110-2, . . . 110-12 can bedisposed on. The frame 108 can be formed from a fluorolucent and/orradiopaque material in some embodiments. The frame 108 can be anenclosure, in some embodiments, as discussed in relation to FIG. 5B. Theframe 108 can include a fluoro window 112 that can allow for x-rays topass through a center of the frame 108 undisturbed by the frame 108and/or by the magnetic transmitting elements 110-1, 110-2, . . . 110-12,thus allowing for an undisturbed fluoroscopy image. In some embodiments,the fluoro window 112 can be a square, as depicted. However, the fluorowindow 112 can be any shape including a circle, square, triangle, etc.

In some embodiments, since the x-rays can pass through the fluoro window112, the frame 108 can be formed from a radiopaque material because thatportion of the magnetic transmitting assembly 106 will be outside of thefluoro window 112 and will not be visible in the fluoroscopy image. Insome embodiments, the frame 108 can be formed of a non-metallic material(e.g., fiberglass). In some embodiments, the fluoro window 112 can be acutout of the frame 108, as discussed herein. Alternatively, the fluorowindow 112 can be formed from a material that is translucent ortransparent in the fluoroscopy image.

In some embodiments, the plurality of electromagnetic transmittingelements 110-1, 110-2, . . . 110-12 can be equidistant from a center ofthe fluoro window 112 or as close to equidistant from the center of thefluoro window 112, as allowed by design. The plurality ofelectromagnetic transmitting elements 110-1, 110-2, . . . 110-12 can beflat copper coils and can be formed from a printed circuit boardfabrication process. In an example, the electromagnetic transmittingelements 110-1, 110-2, . . . 110-12 can be non-fluorolucent. Each of theplurality of electromagnetic transmitting elements 110-1, 110-2, . . .110-12 can allow for a plurality of layers of windings to be formed oneach of the electromagnetic transmitting elements 110-1, 110-2, . . .110-12. In an example, each of the plurality of electromagnetictransmitting elements 110-1, 110-2, . . . 110-12 can have up to 32layers of windings. However, in some embodiments, additional layers ofwindings can be provided (e.g., 64 layers of windings, 128 layers ofwindings, hundreds of layers of windings).

The plurality of electromagnetic transmitting elements 110-1, 110-2, . .. 110-12 can be disposed on an upper portion 111-1 of the frame 108 anda lower portion 111-2 of the frame 108, with respect to the page, insome embodiments. Additionally, the electromagnetic transmittingelements 110-1, 110-2, . . . 110-12 can be disposed on a left side 109-1of the frame 108 and a right side 109-2 of the frame 108, with respectto the page, although not shown. In some embodiments, when theelectromagnetic transmitting elements 110-1, 110-2, . . . 110-12 aredisposed on the lower portion of the frame 108 and the upper portion ofthe frame 108, the upper portion of the frame 108 and the lower portionof the frame 108 can be wider than the side portions of the frame thatconnect the upper portion and the lower portion. In some embodiments(not shown), the magnetic transmitting elements 110-1, 110-2, . . .110-12 can be arranged in an upper arc-like segment and a lower arc-likesegment. In some embodiments, each arc-like segment can be equidistantfrom a center of the fluoro window. As such, each of the magnetictransmitting elements 110-1, 110-2, . . . 110-12 can remain equidistantfrom the center of the fluoro window 112.

In some embodiments, as depicted, the upper set of magnetic transmittingelements 110-1, 110-2, . . . 110-6 can be arranged in a v-shape and thelower set of magnetic transmitting elements 110-7, 110-8, . . . 110-12can be arranged in a v-shape, as shown. In an example, the upper set ofmagnetic transmitting elements 110-1, 110-2, . . . 110-6 can be disposedalong lines bb and cc. For instance, the magnetic transmitting elements110-1, 110-2, 110-3 can be disposed along the line bb and the magnetictransmitting elements 110-4, 110-5, 110-6 can be disposed along the linecc.

The lower set of magnetic transmitting elements 110-7, 110-8, . . .110-12 can be disposed along lines dd and ee. For instance, the magnetictransmitting elements 110-7, 110-8, 110-9 can be disposed along the linedd and the magnetic transmitting elements 110-10, 110-11, 110-12 can bedisposed along the line ee. Although the upper set of magnetictransmitting elements 110-1, 110-2, . . . 110-6 is shown as includingsix magnetic transmitting elements and the lower set of magnetictransmitting elements 110-7, 110-8, . . . 110-12 is shown as includingsix magnetic transmitting elements, each set of magnetic transmittingelements can include more than six magnetic transmitting elements orless than six magnetic transmitting elements. In some embodiments, eachset of magnetic transmitting elements can include from 3 to 8 magnetictransmitting elements.

The lines bb and cc and lines dd and ee can be disposed at angles withrespect to one another such that magnetic transmitting elements 110-1,110-2, . . . 110-112 surround or partially surround the fluoro window112. For example, the lines bb and cc can be disposed at an angle θ withrespect to one another and the lines dd and ee can be disposed at anangle θ′ with respect to one another. In some embodiments, the angles θand θ′ can be the same. In some embodiments, the angles θand θ′ can bein a range from 90 to 180 degrees. Because the magnetic transmittingelements 110-1, 110-2, . . . 110-12 surround or partially surround thefluoro window 112, a more uniform magnetic field is produced within thefluoro window 112 and areas that are located above the fluoro window 112(e.g., area of interest 38 where a patient's chest may be located),allowing for a more uniform magnetic field for use with position sensors28 (e.g., magnetic sensors) that are placed within the fluoro window112.

One or more fluorolucent magnetic transmitting elements can be disposedbetween the magnetic transmitting elements 110-1, 110-2, . . . 110-12within the fluoro window 112. In some embodiments, a magnetictransmitting array, as discussed in relation to FIG. 4A, can be disposedbetween the magnetic transmitting elements 110-1, 110-2, . . . 110-12within the fluoro window 112. As discussed herein, the magnetictransmitting assembly 106 can supplement a magnetic field produced bythe magnetic transmitting elements 110-1, 110-2, . . . 110-12.Alternatively, a different arrangement of fluorolucent magnetictransmitting elements, as discussed in relation to FIG. 3D can be placedin the fluoro window 112. For example, an arrangement of fluorolucentmagnetic transmitting elements, as discussed in relation to FIG. 6, canbe placed in the fluoro window 112.

FIG. 5B is a diagrammatic cross-sectional view along line ff of amagnetic transmitting element 110-2′ in an enclosure 122, which can beincluded in the magnetic transmitting assembly 106 in FIG. 5A, inaccordance with embodiments of the present disclosure. Although theabove discussion is with respect to magnetic transmitting element110-2′, the following discussion applies to all of the magnetictransmitting elements 110-1, 110-2, . . . 110-12 (also referred toherein as magnetic transmitting elements 110) discussed in relation toFIG. 5A. In some embodiments, one or more of the magnetic transmittingelements 110 can be housed inside of one or more enclosures 122. Forexample, the magnetic transmitting element 110-2′ can be housed in theenclosure 122. In an example, each magnetic transmitting element 110 canbe housed inside of an individual enclosure. In some embodiments,multiple magnetic transmitting elements 110 can be housed inside of anenclosure. The enclosure 122 can include a base 124 to which themagnetic transmitting element 110 is mounted. In some embodiments, theenclosure can be mounted on the frame 108′. The enclosure 122 caninclude outer walls 126, 128 that extend vertically from the base 124and are connected to a top 130, which serves to enclose the magnetictransmitting element 110-2′. The base 124 of the enclosure can be in ashape of a square, rectangle, triangle, circle, etc. and can be formedfrom a material such as, for example, fiberglass. In some embodiments,the top 130 can be the same shape as the base.

In some embodiments, a wedge 132 can be placed under the magnetictransmitting element 110-2′ to cause the magnetic transmitting element110-2′ to be disposed at an angle. In some embodiments, the magnetictransmitting element 110-2′ can be disposed at an angle θ″ in a rangefrom 1 to 20 degrees, 2 to 10 degrees, or 3 to 7 degrees; although themagnetic transmitting element 110-2′ can be disposed at an angle that isless than 1 degree or greater than 20 degrees in some embodiments. In anexample, the angle at which the magnetic transmitting element 110-2′ isdisposed can be limited by a desired thickness of the magnetictransmitting assembly 106. For example, the magnetic transmittingassembly 106 can be placed underneath a mattress associated with apatient examination table. If the angle at which the magnetictransmitting elements 110-2′ are disposed is too great, a thickness ofthe magnetic transmitting assembly 106 can be such that it may protrudefrom the patient examination table by an amount that causes it to benoticeable to a patient and cause discomfort.

In some embodiments, each of the magnetic transmitting elements 110 canbe disposed at an angle with respect to the base 124. For example, asdiscussed herein, the magnetic transmitting element 110-2′ can bedisposed at an angle θ″ via the wedge 132. In some embodiments, all ofthe magnetic transmitting elements (e.g., 110-1, 110-2, . . . 110-12)can be disposed at the angle θ″. While each of the magnetic transmittingelements 110 can be disposed at the same angle θ″, each magnetictransmitting element 110 can have a different directionality. Forexample, each magnetic transmitting element 110 can be disposed at thesame angle θ″ around the fluoro window 112, such that a magnetic fieldvector (e.g., B-field vector) produced by each of the magnetictransmitting elements 110 is directed toward the fluoro window 112. Forinstance, each of the magnetic transmitting elements 110 can be disposedat the same angle θ″, such that the magnetic field vector produced byeach of the magnetic transmitting elements 110 is directed toward acommon point located in the area of interest 38. In some embodiments,each of the magnetic transmitting elements 110 can be disposed at thesame angle θ″, such that the magnetic field vector produced by each ofthe magnetic transmitting elements 110 is directed toward a common pointlocated in the area of interest 38 (FIG. 2). In either case, themagnetic transmitting elements 110 should be directed in a way thatcauses a magnetic field to be formed in the area of interest 38.

In some embodiments, the angle θ″ can be perpendicular to the line bbdepicted in FIG. 5A. For example, the magnetic transmitting elements110-1, 110-2, 110-3 can be disposed at the same angle θ″ and with a samedirectionality. In some embodiments, the magnetic transmitting elements110-4, 110-5, 110-6 can be disposed at the same angle θ″, but with adifferent directionality as opposed to magnetic transmitting elements110-1, 110-2, 110-3. For example, the angle θ″ at which each of themagnetic transmitting elements 110-4, 110-5, 110-6 is disposed can beperpendicular to the line cc depicted in FIG. 5A. In some embodiments,the magnetic transmitting elements 110-7, 110-8, 110-9 can be disposedat the same angle θ″, but with a different directionality as opposed tomagnetic transmitting elements 110-1, 110-2, 110-3 and magnetictransmitting elements 110-4, 110-5, 110-6. For example, the angle θ″ atwhich each of the magnetic transmitting elements 110-7, 110-7, 110-9 isdisposed can be perpendicular to the line dd depicted in FIG. 5A. Insome embodiments, the magnetic transmitting elements 110-10, 110-11,110-12 can be disposed at the same angle θ″, but with a differentdirectionality as opposed to magnetic transmitting elements 110-1,110-2, 110-3, 110-4, 110-5, 110-6, 110-7, 110-7, and 110-9. For example,the angle θ″ at which each of the magnetic transmitting elements 110-10,110-11, 110-12 is disposed can be perpendicular to the line ee depictedin FIG. 5A.

FIGS. 5C to 5H depict x-ray sources 133 and x-ray image intensifiers 134at various positions with respect to a patient's body 135, in accordancewith embodiments of the present disclosure. As depicted in FIG. 5C, anx-ray beam emitted from the x-ray source 133-1 is directed through aright anterior oblique 60 degree angle with respect to a line extendingperpendicular from an examination table 136-1 on which the patient 135-1is laying. As depicted in FIG. 5D and 5F, an x-ray beam emitted from thex-ray source 133-2 is directed at a 0 degree angle with respect to aline extending perpendicular from an examination table 136-2 on whichthe patient 135-2 is laying. As depicted in FIG. 5E, an x-ray beamemitted from the x-ray source 133-3 is directed at a left anterioroblique 40 degree angle with respect to a line extending perpendicularfrom an examination table 136-3 on which the patient 135-3 is laying. Asdepicted in FIG. 5G, an x-ray beam emitted from the x-ray source 133-4is directed at a cranial 30 degree angle with respect to a lineextending perpendicular from an examination table 136-4 on which thepatient 135-4 is laying. As depicted in FIG. 5H, an x-ray beam emittedfrom the x-ray source 133-5 is directed at a caudal 20 degree angle withrespect to a line extending perpendicular from an examination table136-5 on which the patient 135-5 is laying.

With further reference to FIGS. 5A to 5H, in some embodiments,non-fluorolucent magnetic transmitting elements 110 may not be disposedon either side 109-1, 109-2 of the frame 108, depicted in FIG. 5A. Insome embodiments, by excluding magnetic transmitting elements 110 frombeing disposed on either side 109-1, 109-2 of the frame 108, x-rays canpass through either side of the frame 108 when the x-ray source 133 andthe image intensifier are disposed at angles similar to those depictedin FIGS. 5C and 5E. For example, because the x-ray source 133 isdisposed at an angle in FIG. 5C and FIG. 5E, this can cause either side109-1, 109-2 of the frame 108 to be disposed between the x-ray source133 and the image intensifier 134. If non-fluorolucent magnetictransmitting elements were included on either side 109-1, 109-2 of theframe 108, a fluoroscopic image may be obstructed. In some embodiments,to account for the positioning of the x-ray source 133, fluorolucentmagnetic transmitting elements, such as those discussed in relation toFIG. 3C can be disposed on either side of the frame 108.

In some embodiments, with further reference to FIGS. 5A to 5H, themagnetic transmitting elements 110 can be disposed in a pattern that isv-shaped, as depicted in FIG. 5A or along an arc-like segment (notdepicted). By arranging the magnetic transmitting elements 110 in av-shape or arc-like segment, the x-rays can pass through the frame 108in between each arm of the v-shape (e.g., defined by lines bb and cc orlines dd and ee) or arc-like segment, when the x-ray source 133-4, 133-5is disposed in positions depicted in FIGS. 5G and 5H. For example, whenthe x-ray source 133-4, 133-5 is disposed in positions depicted in FIGS.5G and 5H, a portion of the frame 108 that is located in between eacharm of the v-shape can be disposed between the x-ray source 133-4, 133-5and each respective image intensifier 134-4, 134-5. This can allow for afluoroscopic image that is unobstructed by the magnetic transmittingelements 110.

FIG. 6 depicts a top view of a third embodiment of a magnetictransmitting assembly 140, in accordance with embodiments of the presentdisclosure. The magnetic transmitting assembly 140 can include a frame142, in some embodiments. The frame 142 can be formed from afluorolucent and/or radiopaque material in some embodiments. The frame142 can be an enclosure, in some embodiments, as discussed in relationto FIG. 5B. In some embodiments, the frame 142 can be a rectangle, asdepicted, and the frame 142 can include a square cutout where the fluorowindow 144 is located. Alternatively, instead of a cutout where thefluoro window 144 is located, the fluoro window can include afluorolucent material that allows x-rays to pass through unobstructed.

In some embodiments, a plurality of electromagnetic transmittingelements 146-1, 146-2, . . . 146-12 can be disposed on the frame 142.The electromagnetic transmitting elements 146-1, 146-2, . . . 146-12 canbe flat copper coils, in some embodiments, and can be disposed aroundthe outside of the fluoro window 144 so they are not visible on anx-ray. As discussed in relation to FIG. 5A, the electromagnetictransmitting elements 146-1, 146-2, . . . 146-12 can benon-fluorolucent. Because the electromagnetic transmitting elements146-1, 146-2, . . . 146-12 are disposed outside of the fluoro window,the fluoroscopy image can remain unobstructed by the electromagnetictransmitting elements 146-1, 146-2, . . . 146-12.

A first row of electromagnetic transmitting elements 146-5, 146-6 can bedisposed on a first side of the fluoro window 144 and a second row ofelectromagnetic transmitting elements 146-7, 146-8 can be disposed on asecond side of the fluoro window 144, opposite the first side. The firstrow of magnetic transmitting elements 146-5, 146-6 can be parallel withthe second row of magnetic transmitting elements 146-7, 146-8 and spacedfrom a center of the fluoro window 144 a same distance as the second rowof magnetic transmitting elements 146-7, 146-8. For example,corresponding magnetic transmitting elements in the first and secondrows (e.g., magnetic transmitting element 146-6 and magnetictransmitting element 146-7) can be equally spaced from the center of thefluoro window 144.

In some embodiments, a third row of magnetic transmitting elements146-1, 146-2, 146-3, 146-4 can be disposed on the first side of thefluoro window 144 and a fourth row of magnetic transmitting elements146-9, 146-10, 146-11, 146-12 can be disposed on the second side of thefluoro window 144, opposite the first side. The third row of magnetictransmitting elements 146-1, 146-2, 146-3, 146-4 can be parallel withthe fourth row of magnetic transmitting elements 146-9, 146-10, 146-11,146-12 and spaced from a center of the fluoro window 144 a same distanceas the fourth row of magnetic transmitting elements 146-9, 146-10,146-11, 146-12. For example, corresponding magnetic transmittingelements in the third and fourth rows (e.g., magnetic transmittingelement 146-3 and magnetic transmitting element 146-10) can be equallyspaced from the center of the fluoro window 144.

In some embodiments, the first, second, third, and fourth rows ofmagnetic transmitting elements 146-1, 146-2, . . . 146-12 can beparallel with one another. In some embodiments, as depicted, the first,second, third, and fourth rows of magnetic transmitting elements 146-1,146-2, . . . 146-12 can be parallel with an edge of the fluoro window144 located on the first side and the second side.

In some embodiments, a spacing between magnetic transmitting elements ineach of the first and second rows can be greater than a spacing betweenmagnetic transmitting elements in each of the third and fourth rows. Forexample, a spacing between a central origin of each magnetictransmitting element 146-5, 146-6 in the first row can be greater than aspacing between a central origin of each magnetic transmitting element146-1, 146-2, 146-3, 146-4 in the third row. In some embodiments, thespacing between the central origin of each magnetic transmitting element146-5, 146-6 in the first row can be 1.25 to 2 times greater than thespacing between the central origin of each magnetic transmitting element146-1, 146-2, 146-3, 146-4 in the third row. The ratio of spacingbetween central origins of the magnetic transmitting elements in thesecond and fourth rows can be the same or similar to the spacing betweenthe central origins of the magnetic transmitting elements in the firstand second rows.

In some embodiments, the spacing between the central origins of eachmagnetic transmitting element 146-1, 146-2 in the first row can be thesame as the spacing between the central origins of each magnetictransmitting element 146-7, 146-8 in the second row. Further, thespacing between the central origins of each magnetic transmittingelement 146-1, 146-2, 146-3, 146-4 in the third row can be the same asthe spacing between the central origins of each magnetic transmittingelement 146-9, 146-10, 146-11, 146-12 in the fourth row. The equalspacing between each of the magnetic transmitting elements can helpproduce a uniform magnetic field throughout the area of interest 38, insome embodiments. In some embodiments, spacing between the first andsecond row magnetic transmitting elements can be the same or similar andthe spacing between the third and fourth row magnetic transmittingelements can be the same or similar to produce the uniform magneticfield. In some embodiments, the magnetic transmitting elements 146-1,146-2, . . . 146-12 can be disposed at an angle, as discussed inrelation to FIG. 5B to create field diversity.

In contrast to FIG. 5A, in some embodiments, fluorolucent magnetictransmitting elements can be disposed within the fluoro window 144. Asdepicted, four fluorolucent magnetic transmitting elements 148-1, 148-2,148-3, 148-4 can be disposed in the fluoro window 144. In someembodiments, the fluorolucent magnetic transmitting elements 148-1,148-2, 148-3, 148-4 can be similar to or the same as those depicted anddiscussed in relation to FIG. 3C. The fluorolucent magnetic transmittingelements 148-1, 148-2, 148-3, 148-4 can be disposed in a grid pattern,as depicted, with a central origin of each of the fluorolucent magnetictransmitting elements 148-1, 148-2, 148-3, 148-4 aligned with a cornerof a square. The central origins of the fluorolucent magnetictransmitting elements 148-1, 148-2, 148-3, 148-4 can be arranged inother patterns, for example, a rectangle, triangle, etc. In someembodiments, the central origins of the fluorolucent magnetictransmitting elements can be equidistant from a center of the fluorowindow 144.

In some embodiments, fewer than four fluorolucent magnetic transmittingelements can be disposed in the fluoro window 144 or more than fourfluorolucent magnetic transmitting elements can be disposed in thefluoro window 144. In some embodiments, the number of fluorolucentmagnetic transmitting elements disposed in the fluoro window 144 can bein a range from 1 to 12. In some embodiments, the number of fluorolucentmagnetic transmitting elements disposed in the fluoro window 144 can bein a range from 3 to 10. In some embodiments, the magnetic transmittingassembly 90, as discussed in relation to FIG. 4A, can be disposed in thefluoro window 144. In some embodiments, the fluorolucent magnetictransmitting elements 148-1, 148-2, 148-3, 148-4 can be disposed on thesame plane as that of the magnetic transmitting elements 146-1, 146-2, .. . 146-12.

In some embodiments, the spacing between a central origin of eachmagnetic transmitting element in the first row of magnetic transmittingelements 146-5, 146-6 (e.g., geometric centers of each of the magnetictransmitting elements 146-5, 146-6) can be the same as a spacing betweena central origin of the fluorolucent magnetic transmitting elements148-1, 148-3. In addition, the spacing between the central origin of thefirst row of magnetic transmitting elements 146-5, 146-6 and between thecentral origin of the fluorolucent magnetic transmitting elements 148-1,148-3 can be the same as a spacing between a central origin of thesecond row of magnetic transmitting elements 146-5, 146-6 and between acentral origin of the fluorolucent magnetic transmitting elements 148-2,148-4. In some embodiments, a central origin of each of the magnetictransmitting elements 146-6, 146-7 and fluorolucent transmittingelements 148-3, 148-4 can be in line with one another, as depicted inFIG. 6. In some embodiments, a central origin of each of the magnetictransmitting elements 146-5, 146-8 and fluorolucent transmittingelements 148-1, 148-2 can be in line with one another, as depicted inFIG. 6.

In some embodiments, the fluoro window 144 can be formed from afluorolucent material. In some embodiments, the fluorolucent materialcan be a polyimide. The fluorolucent material can prevent or reduceinterference with a fluoroscopy image. In an example, the patient can bepositioned on the patient examination table such that their heart ispositioned above the fluoro window 144 in the area of interest 38 (FIG.2). The magnetic field produced by the magnetic transmitting elements146-1, 146-2, . . . 146-12 and fluorolucent magnetic transmittingelements 148-1, 148-2, 149-3, 148-4 can be used to provide a magneticnavigation field for use with position sensors 28 disposed within acatheter, in an example. In addition, fluoroscopic images of the heartcan be captured with little to no interference caused by thefluorolucent material, which forms the fluoro window 144 or thefluorolucent magnetic transmitting elements.

In some embodiments, one or more twisted cabling 145 can provide powerto each one of the magnetic transmitting elements 146-1, 146-2, . . .146-12 or fluorolucent magnetic transmitting elements 148-1, 148-2,148-3, 148-4. A plurality of leads 147, 149 can be connected to the oneor more twisted cabling 145 to provide power to each one of the magnetictransmitting elements 146-1, 146-2, . . . 146-12 or fluorolucentmagnetic transmitting elements 148-1, 148-2, 148-3, 148-4. Each lead147, 149 can include one or more wires configured to provide power to arespective magnetic transmitting element 146-1, 146-2, . . . 146-12 orfluorolucent magnetic transmitting element 148-1, 148-2, 148-3, 148-4.For example, lead 147 can provide power to magnetic transmitting element146-5 and lead 149 can provide power to fluorolucent transmittingelement 148-1. As depicted, the other magnetic transmitting elements andfluorolucent magnetic transmitting elements can include their ownrespective leads that are configured to provide power.

In some embodiments, a power source and/or controller can be connectedto a connector 151 to provide power to and/or control of thefluorolucent magnetic transmitting elements 148-1, 148-2, 148-3, 148-4and/or magnetic transmitting elements 146-1, 146-2, . . . 146-12. In anexample, the medical positioning system 14 (FIG. 1A) can be connected tothe connector.

As discussed herein, multiple drive coils can be used instead of asingle coil to create a magnetic transmitting array. As used herein, adrive coil can include a magnetic transmitting element, which can befluorolucent and/or non-fluorolucent as discussed in relation to FIGS.4, 5A, and 6. The magnetic transmitting element can be driven to createa magnetic field. In some embodiments, multiple drive coils can providea sufficient spatially-unique and orientation-unique signal (e.g.,excitation signal, magnetic field) at any point in 3D space where it isdesired to determine the location and orientation of an electromagneticposition sensor. The unique signals can be created using a specificfrequency to excite each drive coil, although time domain methods canalternatively be employed, which can transmit the same frequency atdifferent time points. An electromagnetic position sensor amplifier andsignal processor can measure a unique amplitude value attributable toeach drive coil (in the case of frequency division multiplexing,synchronous demodulation for example, can be used).

In a system including multiple drive coils, it can be advantageous thatexcitation from one drive coil does not couple into adjacent drive coilsand then re-radiate from those coils, as this may confound thesubsequent means to derive accurate location of the sense coils.Assuming the method of exciting each coil with a unique frequency, thedesired physical behavior which leads to the simplest mathematical modelis that each frequency only represents emanation from a single drivecoil at its (known apriori) location. Coupling and re-radiating fromneighbor coils is undesirable.

Locating and orienting a sensing coil can require three degrees offreedom for the location, and two degrees of freedom for orientation(sometimes denoted pitch and yaw, and noting that the ‘rotation’ of asolenoidal sense coil is not solved for as it is symmetric). This canmean that a minimum of five drive coils can be required. More than fivecoils can be useful for solving for additional parameters such as systemgain, or for extending the viable sensing region.

Multiple fluorolucent magnetic transmitting elements, as describedherein, can be fairly easy to replicate and drive with uniquefrequencies. However, conventional solenoidal drive coils can haveinductances in 10's of millihenries, and are typically paired with aseries capacitor to create a tuned resonant circuit at the desired drivefrequency for that particular coil. A side benefit of the conventionalarrangement is that a resonant coil presents a higher impedance to otherfrequencies such as those used in adjacent coils. This can reduce itssusceptibility to unwanted coupling of excitation signals fromneighboring coils. In the case of the fluorolucent magnetic transmittingelements, as described herein, the inductance can be lower. For example,the fluorolucent magnetic transmitting element can have an inductance ina range from 0.1 to 4 millihenry. In some embodiments, the fluorolucentmagnetic transmitting element can have an inductance of around 0.25millihenries. Conventional drive coils driven with a resonant circuitcan only be driven at the resonant frequency. Low inductance coils(e.g., fluorolucent magnetic transmitting elements) as described in thepresent disclosure can be driven at many different frequencies,simultaneously. This can allow for the same physical assembly (e.g.,fluorolucent magnetic transmitting element) to simultaneously be drivenwith high frequencies to achieve a high signal to noise ratio whilesimultaneously being driven with low frequencies to characterize theenvironment. The low inductance coils, as described in embodiments ofthe present disclosure, also make manufacturing more robust because useof resonant circuits require capacitance matching. Capacitance matchingcan be uniquely done for each transmitter coil and can add time, cost,and variance to manufacturing. As low-inductance coils do not requireresonant circuits, they also do not require capacitance matching, savingtime and money while also resulting in tighter electrical tolerances.

FIG. 7 depicts a schematic view of a first embodiment of a drive circuit152 for a fluorolucent magnetic transmitting element, in accordance withembodiments of the present disclosure. The drive circuit 152 can be amodified Howland drive circuit, in some embodiments. In someembodiments, the drive circuit 152 can be a high impedance drive circuitused for driving a fluorolucent magnetic transmitting element, such asthat discussed in relation to FIG. 3C. As further discussed herein,where a plurality of fluorolucent magnetic transmitting elements arebeing driven, each fluorolucent magnetic transmitting element can bedriven by a separate drive circuit 152. With reference to FIG. 7, analternating current (e.g., sine waveform) can be supplied to the drivecircuit 152 via an input 154 at a desired frequency. In someembodiments, the frequency can be in a range from 1 to 20 kilohertz in asine waveform, although the frequency can be greater than 20 kilohertzor less than 1 kilohertz. The input 154 can be generated by adigital-to-analog converter in some embodiments (not shown). The input154 can be provided to an input resistor 156 that is electricallyconnected to the input 154. The input resistor 156 can have a resistanceof 1 kilohm, in some embodiments, although the resistor can have aresistance that is greater than or less than 1 kilohm. The inputresistor 156 can be part of a low-pass smoothing filter along with aninput capacitor 160. The input resistor 156 and the input capacitor 160can be chosen together to form an RC low-pass filter to give a desiredpole. Practically, the cutoff should be somewhere at least twice thefrequency of the voltage input 154. In some embodiments, a cutofffrequency associated with the RC low-pass filter can be approximatelytwice the frequency of the input 154, but less than half of thedigital-to-analog sampling rate. In some embodiments, an output of theinput resistor 156 can be coupled (e.g., electrically coupled) to anon-inverting input of an input operational amplifier 158. A firstcapacitor can also be coupled to the output of the input resistor 156 toserve as a smoothing pole, in some embodiments. The smoothing pole canhave a frequency in a range from 10 kilohertz to 60 kilohertz, in someembodiments. In an example, the smoothing pole can have a frequency ofapproximately 48 kilohertz. In some embodiments, the input capacitor 160can be coupled to a ground 162.

In some embodiments, the input operational amplifier 158 can beconfigured for unity gain, acting as a buffer circuit. In someembodiments, the input operational amplifier 158 can be an AD823ARoperational amplifier manufactured by Analog Devices, Inc. The output ofthe input operational amplifier 158 can be coupled to an inverting inputof a Howland current source 164. The Howland current source 164 caninclude a first Howland resistor 168-1 coupled between the output of thefirst operational amplifier and an inverting input of a Howlandoperational amplifier 166 of the Howland current source 164. In someembodiments, the Howland current source can be an AD8276ARMZ operationalamplifier manufactured by Analog Devices, Inc. Additionally, the Howlandcurrent source 164 can include a second Howland resistor 168-2 coupledin series with the first Howland resistor 168-1 and the inverting inputof the Howland operational amplifier 166 of the Howland current source164. The Howland current source 164 can include a non-inverting inputcoupled between a third Howland resistor 168-3 and a fourth Howlandcurrent resistor 168-4. The third Howland resistor 168-3 can be coupledto a second ground 170 and the fourth Howland resistor 168-4 can becoupled to an inverting input of an output operational amplifier 172.

The Howland resistors 168-1, 168-2, 168-3, 168-4 can be 40 kilohms andcan be rated as trimmed to better than 0.02 percent matching. In someembodiments, an output of the Howland operational amplifier 166 of theHowland current source 164 can be coupled with a non-inverting input ofthe output operational amplifier 172, which is in a follow configurationto supply desired current levels. The output operational amplifier 172can be an OPA548T operational amplifier manufactured by TexasInstruments.

In some embodiments, an output of the output operational amplifier 172can be coupled with an output resistor 174. The output resistor 174 canhave a resistance of 10 Ohms, in some embodiments. An output of theoutput resistor 174 can be coupled with a phase lead capacitor 175 andan output of the phase lead capacitor 175 can be coupled to the secondHowland resistor 168-2. The output of the output resistor 174 canadditionally be coupled with a fluorolucent magnetic transmittingelement 169, as discussed herein, that includes a load represented by aresistance 176 and an inductance 177, in some embodiments. In anexample, the resistance 176 can be 14.5 Ohms and the inductance 177 canbe 1 millihenry. In some embodiments, the phase lead capacitor 175 canbe selected to match (e.g., correspond with) an inductance 177 (e.g.,inductance) of the fluorolucent magnetic transmitting element. Forexample, the phase lead capacitor 175 can have a capacitance of 10nanofarads, which can match an inductance 177 of 1 millihenry. However,the capacitance of the phase lead capacitor 175 can vary with respect tothe inductance 177 of the fluorolucent magnetic transmitting element. Insome embodiments, where the fluorolucent magnetic transmitting elementhas an inductance 177 of 0.25 millihenry or less, a phase lead capacitormay not be needed.

In some embodiments, the fluorolucent magnetic transmitting element canhave a resistance 176 that is greater than or less than 14.5 Ohms and aninductance 177 that is greater than or less than 1 millihenry. In someembodiments, the inductance 177 can be in a range of from 0.1 to 4millihenry or in a range from 0.1 to 2 millihenry. The resistance 176and the inductance 177 are illustrated as in series with the output ofthe output resistor 174, thus representing the load of the fluorolucentmagnetic transmitting element. In some embodiments, a ballast 178 can becoupled between the load 177 and a ground 179. In some embodiments,fluorolucent magnetic transmitting elements can each be driven by aseparate drive circuit 152.

As discussed, the Howland current source 164 can be modified byintroducing a phase lead via the phase lead capacitor 175 to achieve ahigh output impedance as measured at the input to the fluorolucentmagnetic transmitting element 169, while driving a flat coil load (e.g.,fluorolucent magnetic transmitting element). In some embodiments, thehigh output impedance can be defined as an impedance in a range from 10kilohms to 100 kilohms. However, the impedance can be less than 10kilohms or greater than 100 kilohms. By achieving a high outputimpedance, coupling between neighboring magnetic transmitting elements(e.g., copper coils) can be reduced. For example, driving thefluorolucent magnetic transmitting element at high impedance can causethe fluorolucent magnetic transmitting element to be less susceptible tocoupling with the neighboring magnetic transmitting elements. Forexample, as an impedance that each fluorolucent magnetic transmittingelement is driven at increases, frequencies radiating from theneighboring magnetic transmitting elements are less likely to re-radiatefrom the fluorolucent magnetic transmitting element.

Because the phase lead capacitor 175 is a function of amplifierperformance as well as load, the recommended procedure to affix anappropriate value for the phase lead capacitor can be to run asimulation program with integrated circuit emphasis (SPICE) simulationmodel using accurate models for the amplifiers, as well as measuredvalues of inductance and resistance for the coil (load). Outputimpedance can be assessed in the Spice simulation by shorting the input154 (V_(in)) to circuit ground, and connecting a current source with amagnitude (I_(L)) to the load set at the desired drive frequency. Theresultant output voltage (V_(o)) on the load then allows the outputimpedance (Z_(o)) to be calculated: Z_(o)=V_(o)/I_(L). The phase leadcapacitor can be adjusted to maximize Z_(o). Even with the high currentoutput amplifier and a frequency of 10 kilohertz, an output impedance of40 kilohms can be realized.

FIG. 8 depicts a schematic view of a second embodiment of a drivecircuit 180 for a fluorolucent magnetic transmitting element, inaccordance with embodiments of the present disclosure. An alternatedrive circuit to the drive circuit 152 (depicted in FIG. 7) is depictedin FIG. 8. This drive circuit 180 makes use of a current feedback loopto ensure that the current through the coil stays constant.Additionally, a second feedback loop is used for DC closure. Theadvantage of this method over the earlier modified Howland circuit 152is the output impedance is not dependent on the matching resistors andthere is no output resistor (other than a small sense resistor and theintrinsic resistance of the flat coil) that otherwise dissipates power.It can be desirable that the output impedance is not dependent onmatching resistors because matching can require time and money and canintroduce variability as the electrical characteristics change withtemperature and age. Designs that do not require matching resistors maybe easier to manufacture and can have a greater reliability.

Some embodiments can include a method for preventing coil to coilcoupling in an array of magnetic transmitting elements. In someembodiments, the method can include providing a reference signal to amagnetic transmitting element and a low pass filter in parallel. Forexample, in some embodiments, the reference signal can include analternating current (e.g., sine waveform) that can be supplied to thedrive circuit 180 via an input signal source 182 at a desired frequency(or frequencies). The input signal source 182 can provide a referencesignal used to generate a desired signal driven through a fluorolucentmagnetic transmitting element 214, as further discussed below. Asdepicted in FIG. 8, the ground 181 represents a signal reference for thedepicted drive circuit 180.

In some embodiments, the reference signal, which can include a sinewave, can be generated by a digital-to-analog converter (not shown). Thesine wave can be represented as a 10 kilohertz (kHz) source for examplepurposes. The sine wave can be driven into a non-inverting input of afirst operational amplifier 184. However, the sine wave can have afrequency greater than or less than 10 kHz. For example, the sine wavecan have a frequency in a range from 1 to 20 kilohertz. In someembodiments, the sine wave can have a frequency less than 1 kilohertz orgreater than 20 kilohertz. For example, the circuit can scale tofrequencies less than 1 kilohertz or greater than 20 kilohertz based oncircuit components that are selected.

An output of the first operational amplifier 184 can be driven into abuffer circuit, which can be a second operational amplifier 186 that isconfigured for unity gain. An output from the first operationalamplifier 184 also drives a low pass filter circuit, which includes afirst resistor 188 and a first capacitor 190, which leads to a ground192. The first resistor 188 can have a resistance of approximately 100kilohms, although the first resistor 188 can have a resistance less thanor greater than 100 kilohms. The first capacitor 190 can have acapacitance of approximately 0.1 microfarad, although the firstcapacitor 190 can have a capacitance less than or greater than 0.1microfarad. In some embodiments, the capacitance of the first capacitor190 can be determined based on the frequency of the input signal source182 in order to provide a desired attenuation. The low pass filter(e.g., resistor-capacitor circuit) can filter the 10 kilohertz signalsuch that only a direct current value remains.

The direct current value (e.g., direct current offset) may ideally bezero, but may have a small value due to less than ideal circuitbehavior. The direct current value (V_(DC)) can be buffered by a thirdoperational amplifier 194 that is configured for unity gain. In someembodiments, the direct current value (e.g., direct current offset) canprovide a reference for how much attenuation needs to be performed tothe reference signal, as previously discussed, that has passed throughthe magnetic transmitting element. The signal generated by the low passfilter that is buffered by the third operational amplifier 194 providesfor direct current loop closure and a direct current offset with respectto the reference signal.

In some embodiments, the buffer circuit (e.g., second operationalamplifier 186 configured for unity gain) can drive a second capacitor196 in series with a flat coil load 198 and a sense resistor 200. Insome embodiments, the flat coil load can be representative of afluorolucent magnetic transmitting element 214, as discussed herein. Thesecond capacitor's 196 capacitance can be chosen such that itapproximately offsets a reactive impedance of the flat coil load 198,such that a phase angle of a driving circuit of the flat coil load 198is approximately zero. As depicted in FIG. 8, the fluorolucent magnetictransmitting element 214 is depicted without a resistance. In practice,components of the fluorolucent magnetic transmitting element 214 willhave some parasitic component (e.g., resistance); however, forillustration purposes the fluorolucent magnetic transmitting element isdepicted without an associated resistance.

In some embodiments, the second capacitor 196 does not have to have aprecise capacitance value. The sense resistor 200 can be a current senseresistor with approximately 1 Ohm of resistance and can sense thereference signal that has passed through the fluorolucent magnetictransmitting element, although the sense resistor 200 can have aresistance less than or greater than 1 Ohm. In some embodiments, atleast one of a voltage, current, and phase of the reference signal thathas passed through the fluorolucent magnetic transmitting element can besensed. A voltage and phase measured at the sense resistor 200(V_(SENSE)) can correspond to a current and phase of the flat coil load198. In some embodiments, this signal is fed back to a third resistor202 where it is summed with the direct current offset from a fourthresistor 204 to generate an attenuation term and subsequently fed to afourth operational amplifier 206. The fourth operational amplifier 206can be configured as a non-inverting summing amplifier. The output ofthe fourth operational amplifier 206 can be defined through thefollowing equation:

V _(U4)=1+(R6/R5)*((V _(SENSE) +V _(DC))/2)

where V_(U4) is a voltage output of the fourth operational amplifier206. R6 is a resistance of a sixth resistor 208 that is electricallyconnected between an output of the fourth operational amplifier 206 andan inverting input of the fourth operational amplifier 206. R5 can be aresistance of a fifth resistor 210 electrically connected between theinverting input of the fourth operational amplifier 206 and a ground212. V_(SENSE) can be a voltage and phase measured at the sense resistor200 and V_(DC) can be the direct current value. In some embodiments, theresistance of the sixth resistor 208 can be 5 kilohms and theresistances of the third resistor 202, fourth resistor 204, and thefifth resistor 210 can be 1 kilohms each, although the resistances ofthe sixth resistor 208, third resistor 202, fourth resistor 204, fifthresistor 210, and sixth resistor 208 can be less than or greater thanthose resistances discussed herein.

In some embodiments, the output of the fourth operational amplifier 206can be electrically connected to an inverting input of the firstoperational amplifier 184 to close the control loop and to apply theattenuation term to the reference signal to attenuate the referencesignal. Thus, the output of the fourth operational amplifier 206 canfollow the sine wave input in amplitude and phase, as the control loopcan force the voltage sensed at the sense resistor 200 to proportionallyfollow the sine wave input. This can effectively drive out any currentsthat have been coupled from adjacent flat coils. By adjusting resistorvalues and/or the sine wave input amplitude, current through the flatload coil 198 can be set to a desired value.

FIG. 9 depicts a method 220 for determining an attenuation term for anexcitation signal produced by a fluorolucent magnetic transmittingelement, in accordance with embodiments of the present disclosure. Themethod can include driving a fluorolucent magnetic transmitting elementwith a first signal at a first frequency and a second signal at a secondfrequency, wherein the first frequency is lower than the secondfrequency, at block 222. In some embodiments, the first signal can be alow frequency signal in a range from 0.5 kilohertz to 2 kilohertz andthe second frequency can be a high frequency signal in a range from 10kilohertz to 20 kilohertz; and the first and second signal can be usedto drive each fluorolucent magnetic transmitting element. In someembodiments where more than one fluorolucent magnetic transmittingelement is being driven, each transmitting element can be driven at alow and high frequency, however, the low and high frequency at whicheach transmitting element is driven can be unique to each transmittingelement. For instance, where two transmitting elements are being drivenwith low and high frequencies, the low frequencies can be different fromone another and the high frequencies can be different from one another.

Alternatively, as previously discussed, more than two signals can beused to drive each fluorolucent magnetic transmitting element. Upondriving the fluorolucent magnetic transmitting element(s) with the firstand second signals, a first excitation signal (e.g., first magneticfield) can be generated by each fluorolucent magnetic transmittingelement and a second excitation signal (e.g., second magnetic field) canbe generated by each fluorolucent magnetic transmitting element,respectively. In some embodiments, a first received signal and a secondreceived signal can be generated upon receipt of the first excitationsignal and the second excitation signal with a magnetic position sensor(e.g., a magnetic coil, a wound coil). The method can include receivingthe first received signal and the second received signal with acomputer, at block 224.

The low frequency component and the high frequency component of thefirst received signal and the second received signal can be separatedsince the received signals can be combined on receipt with the magneticposition sensor. Separation of the signal components can allow for eachreceived signal component to be analyzed separately. In an example, thelow frequency and high frequency components of the received signals canbe separated by frequency domain multiplexing, in some embodiments. Insome embodiments, a lower frequency (e.g., 1 kilohertz) signal canremain relatively unperturbated by a number of structural materials(e.g., metallic elements), as further discussed in relation to FIG. 10,the lower frequency signal can be used to calibrate a higher frequencysignal, which can be used for navigation. The higher frequency signalcan have a greater responsiveness for navigation, but can be perturbatedby metallic elements (e.g., aluminum, copper, thin steel, thick steel);while the lower frequency signal can cause a more sluggish performancewhen used for navigation. By way of example, a lower frequency signal isreferred to herein as being a signal with a frequency of 1 kilohertz anda higher frequency signal is referred to herein as being a signal with afrequency of 10 kilohertz. However, the lower frequency can have afrequency in a range from 0.5 kilohertz to 2 kilohertz and the higherfrequency signal can have a frequency in a range from 10 kilohertz to 20kilohertz, as previously discussed.

To further illustrate this, FIG. 10 depicts a graph showing a non-linearfrequency-dependent attenuation of a signal generated by a magneticposition sensor in the presence of various metals with respect to freespace (e.g., air), in accordance with embodiments of the presentdisclosure. FIG. 10 is experimental data associated with a non-linearfrequency-dependent attenuation of a signal generated by a magneticposition sensor in the presence of various metals with respect to freespace. The attenuation can be defined as a change in an induced voltagerelative to free space at the same frequency. As used herein,perturbation can be defined as a non-linear frequency-dependentattenuation of a signal generated by a magnetic position sensor in thepresence of various metals with respect to free space.

As depicted, a lower frequency (e.g., 1 kilohertz) can remain relativelyunperturbated by the metallic elements (e.g., aluminum, copper, thinsteel, thick steel). The thin steel was between 0.025 and 0.1millimeters thick and the thick steel was approximately 2 centimetersthick. As depicted, while the signal is less perturbated by aluminumthan the other metallic elements, the signal still becomes perturbatedas the frequency increases. An even more pronounced perturbation isnoticed with regard to copper, thin steel, and thick steel when presentin a magnetic field. For instance, as the frequency increases, theperturbation of the signal increases. In an example, with reference toFIG. 10, relative to free space data set 215, a thick steel data set 216experiences a similar amount of frequency attenuation as that of a thinsteel data set 217 and a copper data set 218. With reference to thealuminum data set 219, the data experiences the least amount offrequency attenuation relative to the free space data set 215.

Challenges can exist when using a lower frequency (e.g., 1 kilohertz)signal for navigation. For example, a greater current can be provided tothe fluorolucent magnetic transmitting element, as opposed to using ahigher frequency (e.g., 10 kilohertz), or a greater area associated withcoils of the fluorolucent magnetic transmitting element can be required.Alternatively, to navigate with a same sort of responsiveness as ahigher frequency (e.g., 10 kilohertz), signal filtering can be performedon the lower frequency signal (e.g., first received signal) to removenoise from the signal. However, filtering of the lower frequency signalcan result in a sluggish performance due to the resources and timerequired for filtering. In accordance with embodiments of the presentdisclosure, filtering can be performed on the lower frequency signalreceived by the position sensor 28 not for navigation purposes, but forcalibrating the higher frequency signal (e.g., second signal) to ametallic environment in proximity to the navigational field.

As depicted in FIG. 10, a voltage induced on a position sensor (e.g.,position sensor 28 ₁ in FIG. 1A and 1B) is a linear function of amagnetic frequency. While 1 kilohertz magnetic fields can become lessperturbated than 10 kilohertz fields, 10 times the current andconsequently 100 times the power dissipation are required to obtain thesame voltage induced on the position sensor 28 with a 1 kilohertz fieldversus a 10 kilohertz field.

Due to the low inductance of some fluorolucent magnetic transmittingelements (e.g., a flat drive coil such as that discussed in relation toFIG. 3C), multiple frequencies can be driven through a singlefluorolucent transmitting element simultaneously, with a unique pair offrequencies (e.g., two frequencies) used for each fluorolucent magnetictransmitting element. However, in some embodiments, greater than twofrequencies can be driven through each fluorolucent transmitting elementsimultaneously. For example, four or more frequencies can be used todrive the single fluorolucent transmitting element simultaneously, whichcan improve a robustness associated with determining a position of amagnetic position sensor and in calculation of an attenuation term; thecalculation of which is further discussed herein. In an example, thefrequency dependence of the attenuation can be described parametrically,so additional measurements (e.g., measurements gathered throughadditional frequencies that are used to drive the fluorolucent magnetictransmitting element) can provide a more robust estimate of theattenuation.

In some embodiments, a low inductance of the fluorolucent magnetictransmitting element can in a range from 0.1 millihenry to 4 millihenryor in a range from 0.1 to 2 millihenry. This is in contrast to a moretraditional transmitter coil (e.g., copper coil), which can prove to bemore difficult to drive multiple frequencies through the coil, since itis of a higher inductance than the fluorolucent magnetic transmittingelement. For example, a more traditional transmitter coil can have aninductance in a range from 15 millihenry to 50 millihenry.

With further reference to FIG. 9, in some embodiments, the method 220can include filtering the first received signal and the second receivedsignal, at block 226, to provide a first filtered and received signaland a second filtered and received signal. In an example, the firstreceived signal (e.g., low frequency signal) and the second receivedsignal (e.g., high frequency signal) can be filtered based on a signalto noise ratio. For instance, the first signal can be highly filtered toachieve an acceptable signal to noise ratio and can be used todynamically calibrate the higher frequency signal, which can be used toprovide accurate navigation of the position sensor 28. For example, thefirst signal can be used to continuously calibrate the higher frequencysignal. In some embodiments, the signal to noise ratio can be in a rangefrom 30 to 90 decibels. In some embodiments, the signal to noise ratiocan be in a range from 40 to 70 decibels. In some embodiments, thesignal to noise ratio can be 45 decibels. The low frequency signal canbe used to probe a navigational domain and can rely on the fact that thelow frequency is relatively unperturbated by the number of structuralmaterials (e.g., metallic objects) that can otherwise impact the highfrequency signal.

In an example, a 10 kilohertz signal can inherently have 10 times therecovered signal amplitude and thus 10 times the signal-to-noise ratioof the 1 kilohertz signal, assuming the drive coils are driven withidentical amplitudes for each frequency. However, in some embodiments,because the 1 kilohertz signal can be used for a more static or regionalcalibration factor, it can be conventionally time domain filtered in arange from 1/10 to 1/100 the bandwidth of the dynamic location resultobtained from the 10 kilohertz signal, thus yielding a suitable orequivalent signal to noise ratio. The heavier filtering can be used onthe 1 kilohertz signal because it only needs to adapt to generallyinfrequent perturbations in the magnetic field (e.g., caused by a changein fluoroscopy head position). A filter settling time of 1 to 3 secondscan be used following such a perturbation. Alternatively, an optimalfilter using statistical methods such as a Kalman filter that accountsfor the higher noise level of the 1 kilohertz signal can be used tocombine the information from both the 1 kilohertz signal and the 10kilohertz signal.

As the structural materials move with respect to the navigational domain(e.g., area of interest 38 (FIG. 2)), filtering can be performed on thelow frequency signal and the high frequency signal and the filtered lowfrequency signal and the filtered high frequency signal can be used todetermine an attenuation term (further defined below) for the higherfrequency signal for use in navigation. For example, the method 220(FIG. 9) can include determining an attenuation term for the secondsignal at the second frequency based on the first filtered and receivedsignal and the second filtered and received signal, at block 228.

In some embodiments, the first received signal and the second receivedsignal can remain unfiltered when determining the attenuation term forthe second signal at the second frequency. Upon determination of theattenuation term from the unfiltered signals, the attenuation term canbe filtered to provide a filtered attenuation term. In some embodiments,this can save processing resources associated with a computer byallowing for one input to be filtered (e.g., the attenuation term) andavoiding the filtering of two or more inputs (e.g., first signal, secondsignal). In cases where more than two signals are used, this can proveto be especially true.

In some embodiments, the attenuation term can be defined via thefollowing equation,

(V₂*ω₁)/(V₁*ω₂)

where V₁ is representative of a first voltage amplitude induced in acoil associated with the first signal; V₂ is representative of a secondvoltage amplitude induced in a coil associated with the second signal;ω₁ is representative of a first frequency associated with the firstsignal; and ω₂ is representative of a second frequency associated withthe second signal. As depicted and discussed in relation to FIG. 8, theattenuation term can be applied to the reference signal via the fourthoperational amplifier 206 to attenuate the reference signal.Accordingly, the method can include determining the attenuation term forthe second received signal at the second frequency based on the firstfiltered and received signal and the second filtered and receivedsignal. For example, with reference to the above equation, theattenuation term can be determined based on a first voltage amplitudeinduced in the fluorolucent magnetic transmitting element associatedwith the first signal and a first frequency associated with the firstsignal; and a second voltage amplitude induced in the fluorolucentmagnetic transmitting element associated with the second signal and asecond frequency associated with the second signal. In an ideal system(e.g., in free-space) where the first frequency and second frequency areunperturbated, the attenuation term can be one. However, whereperturbations are present, the attenuation term can be greater than orless than one.

As a structural material (e.g., magnetic field-disturbing object,metallic object) moves within proximity of the navigational domain, aposition determined from the first signal (e.g., lower frequency signal)that is received by the position sensor 28 ₁ (FIGS. 1A and 1B) canremain approximately the same, while a position determined from thesecond signal (e.g., higher frequency signal) that is received by theposition sensor 28 ₁ can change. Based on the change in position and/orchange in a voltage induced in the position sensor 28 ₁ via the firstreceived signal versus a voltage induced in the position sensor 28 ₁ viathe second received signal, the second received signal can becalibrated. For example, an attenuation term can be determined, aspreviously discussed, which can be used to calibrate the second receivedsignal. In some embodiments, the attenuation term can be applied to thesecond received signal to factor out perturbations in the secondreceived signal (e.g., perturbations caused by structural materials suchas metallic objects). In some embodiments, the attenuation term can beapplied to the second received signal by dividing the second receivedsignal by the attenuation term.

As previously discussed, the attenuation term can be filtered in someembodiments, thus alleviating the need to individually filter the firstreceived signal and the second received signal. Upon filtering of theattenuation term, the attenuation term can be referred to herein as afiltered attenuation term. In some embodiments, the filtered attenuationterm can be applied to the second received signal to compensate thesecond received signal for a perturbation in the second received signal.Upon application of the filtered attenuation term to the second receivedsignal, the second received signal can be referred to as an attenuatedreceived signal. The filtered attenuation term can be applied to thesecond received signal by dividing the second received signal by thefiltered attenuation term to provide the attenuated received signal.

In some embodiments, each received signal can be analyzed to determinethe respective frequency associated with each received signal and astatistical filter can be used along with both high frequency and lowfrequency measurements to determine a high frequency gain relative tofree-space. In some embodiments, the filter can be a Kalman filter. Assuch, corrections can be made for perturbations in tracking accuracywhen metallic objects, such as the C-arm, x-ray emitter, x-ray detector,etc. are moved in a proximity to the navigational domain. In someembodiments, as previously discussed, using the low frequency signalalone for navigation purposes can result in sluggish performance due tothe amount of filtering that is performed on the low frequency signal(e.g., due to a group delay associated with low-pass filtering).However, by the time a magnetic field-disturbing object is moved withrespect to the navigational domain (e.g., area of interest 38 (FIG. 2)),the low frequency signal can be filtered and the higher frequency signalcan be adjusted, based on the filtered low frequency signal, to accountfor any magnetic disturbance caused by the metallic object.

In some embodiments where the first received signal and the secondreceived signal are filtered, the second filtered and received signalcan be adjusted by applying the attenuation term to the second filteredand received signal (e.g., by dividing the second filtered and receivedsignal by the attenuation term) to provide an adjusted second signalcompensated for perturbations via the attenuation term. A positionassociated with the magnetic position sensor can then be determinedbased on the adjusted second signal (e.g., attenuated received signal).

FIG. 11A depicts a diagram of a system 250 for determining anattenuation term for a signal produced by a fluorolucent magnetictransmitting element, according to embodiments of the presentdisclosure. The system 250 can include a data store 252, a determiningattenuation term sub-system 254, and/or a number of engines. Thedetermining attenuation term sub-system 254 can be in communication withthe data store 252. The determining attenuation term sub-system 254 caninclude a number of engines (e.g., drive engine 256, receive engine 258,determine attenuation term engine 260, determine position engine 262,etc.). The determining attenuation term sub-system 254 can includeadditional or fewer engines than illustrated to perform the variousfunctions described herein. The number of engines can include acombination of hardware and programming configured to perform a numberof functions described herein (e.g., receiving, determining, etc.). Eachof the engines can include hardware or a combination of hardware andprogramming designated or designed to execute a module (e.g., aparticular module). The programming can include instructions (e.g.,software, firmware, etc.) stored in a memory resource (e.g.,computer-readable medium) as well as a hard-wired program (e.g., logic).

The determining attenuation term sub-system 254 can include a computingdevice analogous to that discussed herein and with respect to FIG. 11B,which is further discussed below. In some embodiments, the computingdevice can include a digital display such as a graphical user interface(GUI), which is suitable for the display of electronic data. A userinterface can include hardware components and/or computer-readableinstruction components. For instance, hardware components can includeinput components (e.g., a mouse, a touchscreen, a keyboard, dials andbuttons, etc.) and/or output components (e.g., a display, vibrationgenerating devices, speakers, etc.). An example user interface caninclude a GUI, which can digitally represent data associated withdetermining an attenuation term for a signal produced by a fluorolucentmagnetic transmitting element.

The drive engine 256 can include hardware and/or a combination ofhardware and programming to drive the fluorolucent magnetic transmittingelement with a first signal at a first frequency and a second signal ata second frequency to generate a first excitation signal and a secondexcitation signal, wherein the first frequency is lower than the secondfrequency. In some embodiments, as discussed herein, the lower frequencysignal (e.g., first signal) can have a frequency in a range from 0.5kilohertz to 2 kilohertz and the higher frequency signal (e.g., secondsignal) can have a frequency in a range from 10 kilohertz to 20kilohertz. The lower frequency at which the first excitation signal isgenerated can remain relatively unperturbated by metallic elements(e.g., aluminum, copper, thin steel, thick steel) and can thus be usedto calibrate the higher frequency excitation signal. In an example, thefirst excitation signal can be less perturbated by metallic element(s)located proximate to the fluorolucent magnetic transmitting element thanthe second excitation signal. For instance, the first excitation signalcan be less perturbated by a C-arm, x-ray emitter, x-ray detector, etc.located proximate to the fluorolucent magnetic transmitting element.

The receive engine 258 can include hardware and/or a combination ofhardware and programming to receive a first received signal and a secondreceived signal with a computer, the first received signal and thesecond received signal having been generated upon receipt of the firstexcitation signal and the second excitation signal with a magneticposition sensor. In some embodiments, the magnetic position sensor canbe disposed on a catheter (e.g., distal end of a catheter). The magneticposition sensor can be configured to receive the first excitation signaland the second excitation signal generated by the fluorolucent magnetictransmitting element.

The determine attenuation term engine 260 can include hardware and/or acombination of hardware and programming configured to determine anattenuation term for the second received signal at the second frequencybased on the first received signal and the second received signal, aspreviously discussed herein. In some embodiments, the attenuation termfor the second signal can be determined based on a change in positionand/or change in a voltage induced in the magnetic position sensor viathe first received signal versus a change in position and/or a voltageinduced in the magnetic position sensor via the second received signal,as discussed herein.

The determine position engine 262 can include hardware and/or acombination of hardware and programming configured to determine aposition of the magnetic position sensor based on an attenuated receivedsignal, the attenuated received signal having been generated throughapplication of the attenuation term to the second received signal. Insome embodiments, a position of the magnetic position sensor determinedbased on the attenuated received signal can be different than a positionof the magnetic position sensor determined based on the second receivedsignal. For example, the position of the magnetic position sensordetermined based on the attenuated received signal can be corrected forperturbations caused in the magnetic field as a result of theattenuation term being applied to the second received signal.

As discussed herein, the first excitation signal, which can be generatedvia a lower frequency than the second signal, can be less perturbated bya metallic object located proximate to the fluorolucent magnetictransmitting element than the second excitation signal. In someembodiments, a frequency associated with the first signal can be in arange from 0.5 to 2 kilohertz and a frequency associated with the secondsignal can be in a range from 10 to 20 kilohertz.

FIG. 11B depicts a diagram of an example of a computing device 270 fordetermining an attenuation term for a signal produced by a fluorolucentmagnetic transmitting element, according to various embodiments of thepresent disclosure. The computing device 270 can utilize software,hardware, firmware, and/or logic to perform a number of functionsdescribed herein.

The computing device 270 can be a combination of hardware andinstructions to share information. The hardware, for example can includea processing resource 272 and/or a memory resource 276 (e.g.,computer-readable medium (CRM), database, etc.). A processing resource272, as used herein, can include a number of processors capable ofexecuting instructions stored by the memory resource 276. Processingresource 272 can be integrated in a single device or distributed acrossmultiple devices. The instructions (e.g., computer-readable instructions(CRI)) can include instructions stored on the memory resource 276 andexecutable by the processing resource 272 to implement a desiredfunction (e.g., determine an attenuation term for the second receivedsignal at the second frequency based on the first received signal andthe second received signal, etc.).

The memory resource 276 can be in communication with the processingresource 272. The memory resource 276, as used herein, can include anumber of memory components capable of storing instructions that can beexecuted by the processing resource 272. Such memory resource 276 can bea non-transitory CRM. Memory resource 276 can be integrated in a singledevice or distributed across multiple devices. Further, memory resource276 can be fully or partially integrated in the same device asprocessing resource 272 or it can be separate but accessible to thatdevice and processing resource 272. Thus, it is noted that the computingdevice 270 can be implemented on a support device and/or a collection ofsupport devices, on a mobile device and/or a collection of mobiledevices, and/or a combination of the support devices and the mobiledevices.

The memory 276 can be in communication with the processing resource 272via a communication link 274 (e.g., path). The communication link 274can be local or remote to a computing device associated with theprocessing resource 272. Examples of a local communication link 274 caninclude an electronic bus internal to a computing device where thememory resource 276 is one of a volatile, non-volatile, fixed, and/orremovable storage medium in communication with the processing resource272 via the electronic bus.

Link 274 (e.g., local, wide area, regional, or global network)represents a cable, wireless, fiber optic, or remote connection via atelecommunication link, an infrared link, a radio frequency link, and/orother connectors or systems that provide electronic communication. Thatis, the link 274 can, for example, include a link to an intranet, theInternet, or a combination of both, among other communicationinterfaces. The link 274 can also include intermediate proxies, forexample, an intermediate proxy server (not shown), routers, switches,load balancers, and the like.

The memory resource 276 can include a number of modules such as a drivemodule 278, a receive module 280, a determine module 282, and a filtermodule 284. The modules 278, 280, 282, 284 can include CRI that whenexecuted by the processing resource 272 can perform a number offunctions. The modules 278, 280, 282, 284 can be sub-modules of othermodules. For example, the drive module 278 and the receive module 280can be sub-modules and/or contained within the same computing device. Inanother example, the modules 278, 280, 282, 284 can comprise individualmodules at separate and distinct locations (e.g., CRM, etc.).

Each of the modules 278, 280, 282, 284 can include instructions thatwhen executed by the processing resource 272 can function as acorresponding engine, as described herein. For example, the determineattenuation term module 282 can include CRI that when executed by theprocessing resource 272 can function as the determine attenuation termengine 260. For instance, the determine attenuation term module 282 caninclude CRI that when executed by the processing resource 272 can causea computing device to determine an attenuation term for the secondreceived signal at the second frequency based on the first receivedsignal and the second received signal.

FIG. 12 depicts a schematic and block diagram view of an electromagneticnavigation system 300, in accordance with embodiments of the presentdisclosure. The electromagnetic navigation system 300 can be a system inwhich a medical device, such as a guidewire, catheter, introducer (e.g.,sheath) incorporating a magnetic position sensor 302 and/or an electrode304 may be used. With continued reference to FIG. 12, system 300, asdepicted, includes a main electronic control unit 306 (e.g., aprocessor) having various input/output mechanisms 308, a display 310, anoptional image database 312, an electrocardiogram (ECG) monitor 314, alocalization system, such as a medical positioning system 316, a medicalpositioning system-enabled elongate medical device 318, a patientreference sensor 320, a magnetic position sensor 302 and an electrode304. For simplicity, one magnetic position sensor 302 and one electrode304 are shown, however, more than one magnetic position sensor 302and/or more than one electrode 304 can be included in the system 300.

In some embodiments, the system 300 can include a drive circuit incommunication with the medical positioning system 316. The drive circuit322 can include a drive circuit similar to those discussed herein, forexample, those discussed in relation to FIGS. 7 and 8. The drive circuit322 can be in communication with one or more magnetic transmittingelements (MTE) 324, which in some embodiments can be a fluorolucentmagnetic transmitting elements, such as that discussed in relation toFIG. 3C or a non-fluorolucent magnetic transmitting element.

Input/output mechanisms 308 may comprise conventional apparatus forinterfacing with a computer-based control unit including, for example,one or more of a keyboard, a mouse, a tablet, a foot pedal, a switchand/or the like. Display 310 may also comprise conventional apparatus,such as a computer monitor.

Various embodiments described herein may find use in navigationapplications that use real-time and/or pre-acquired images of a regionof interest. Therefore system 300 may optionally include image database312 to store image information relating to the patient's body. Imageinformation may include, for example, a region of interest surrounding adestination site for medical device 318 and/or multiple regions ofinterest along a navigation path contemplated to be traversed by medicaldevice 318. The data in image database 312 may comprise known imagetypes including (1) one or more two-dimensional still images acquired atrespective, individual times in the past; (2) a plurality of relatedtwo-dimensional images obtained in real-time from an image acquisitiondevice (e.g., fluoroscopic images from an x-ray imaging apparatus),wherein the image database acts as a buffer (live fluoroscopy); and/or(3) a sequence of related two-dimensional images defining a cine-loopwherein each image in the sequence has at least an ECG timing parameterassociated therewith, adequate to allow playback of the sequence inaccordance with acquired real-time ECG signals obtained from ECG monitor314. It should be understood that the foregoing embodiments are examplesonly and not limiting in nature. For example, the image database mayalso include three-dimensional image data as well. It should be furtherunderstood that the images may be acquired through any imaging modality,now known or hereafter developed, for example X-ray, ultra-sound,computerized tomography, nuclear magnetic resonance or the like.

ECG monitor 314 is configured to continuously detect an electricaltiming signal of the heart organ through the use of a plurality of ECGelectrodes (not shown), which may be externally-affixed to the outsideof a patient's body. The timing signal generally corresponds to aparticular phase of the cardiac cycle, among other things. Generally,the ECG signal(s) may be used by the control unit 306 for ECGsynchronized play-back of a previously captured sequence of images (cineloop) stored in database 312. ECG monitor 314 and ECG-electrodes mayboth comprise conventional components. Medical positioning system 316 isconfigured to serve as the localization system and therefore todetermine position (localization) data with respect to one or moremagnetic position sensors 302 and/or electrodes 304 and output arespective location reading.

The location readings may each include at least one or both of aposition and an orientation (P&O) relative to a reference coordinatesystem (e.g., magnetic based coordinate system, impedance basedcoordinate system), which may be the coordinate system of medicalpositioning system 316. For some types of sensors, the P&O may beexpressed with five degrees-of-freedom (five DOF) as a three-dimensional(3D) position (e.g., a coordinate in three perpendicular axes X, Y andZ) and two-dimensional (2D) orientation (e.g., a pitch and yaw) of anelectromagnetic position sensor 302 in a magnetic field relative to amagnetic field generator(s) or transmitter(s) and/or electrode 304 in anapplied electrical field relative to an electrical field generator(e.g., a set of electrode patches). For other sensor types, the P&O maybe expressed with six degrees-of-freedom (six DOF) as a 3D position(e.g., X, Y, Z coordinates) and 3D orientation (e.g., roll, pitch, andyaw).

Medical positioning system 316 determines respective locations (e.g.,P&O) in the reference coordinate system based on capturing andprocessing signals received from the magnetic position sensor 302 whilethe sensor is disposed in a controlled low-strength alternating current(AC) magnetic (e.g., magnetic) field produced by the MTE 324 and signalsreceived from the electrode 304 while the electrodes are disposed in acontrolled electrical field generated by electrode patches, for example.In some embodiments, the medical positioning system 316 and/or the maincontrol 306 can include a computing device, as discussed in relation toFIGS. 11A and 11B, which can include hardware and/or a combination ofhardware and programming to determine an attenuation term.

Each magnetic position sensor 302 and the like may comprise a coil and,from an electromagnetic perspective, the changing or AC magnetic fieldmay induce a current in the coil(s) when the coil(s) are in the magneticfield. The magnetic position sensor 302 is thus configured to detect oneor more characteristics (e.g., flux) of the magnetic field(s) in whichit is disposed and generate a signal indicative of thosecharacteristics, which is further processed by medical positioningsystem 316 to obtain a respective P&O for the magnetic sensor 302. Theelectrode 304 may comprise a ring electrode, in some examples. Theelectrode 304 can be configured to detect one or more characteristics(e.g., current) of the electrical field(s) in which it is disposed andgenerate a signal indicative of those characteristics, which is furtherprocessed by medical positioning system 316 to obtain a respective P&Ofor the plurality of electrode 304.

Referring still to FIG. 12, in an embodiment, medical positioning system316 may determine the P&O of medical positioning system enabled medicaldevice 318 according to certain physical characteristics ofelectromagnetic position sensor 302 and electrode 304 in addition to thesignals received from magnetic position sensor 302 and electrode 304.Such characteristics may include predetermined calibration data, forexample, indicative of or corresponding to the respective winding anglesof one or more portions of a coil on sensor 302, the number of coilportions, the type(s) of conductor used in the coil, and the directionand number of loops in the coil. In addition, such characteristics mayinclude predetermined calibration data, for example, indicative of orcorresponding to a position of electrode 304, the number of electrodes304, size of electrode 304, shape of electrode 304, and type ofmaterial(s) the electrodes 304 are formed of. Medical positioning system316 may have such characteristics of the magnetic position sensor 302and/or electrode 304 pre-programmed, may determine such characteristicsfrom a calibration procedure, or may receive such characteristics from astorage element coupled with medical device 318.

Magnetic position sensor 302 and the electrode 304 may be associatedwith medical positioning system enabled medical device 318. Anothermedical positioning system sensor, namely, patient reference sensor(PRS) 320 (if provided in system 300) can be configured to provide apositional reference of the patient's body so as to allow motioncompensation for patient body movements, such as respiration-inducedmovements. Such motion compensation is described in greater detail inU.S. patent application Ser. No. 12/650,932, entitled “Compensation ofMotion in a Moving Organ Using an Internal Position Reference Sensor”,hereby incorporated by reference in its entirety as though fully setforth herein. PRS 320 may be attached to the patient's manubrium sternumor other location. Like the magnetic position sensor 302, PRS 320 can beconfigured to detect one or more characteristics of the magnetic fieldin which it is disposed, wherein medical positioning system 316determines a location reading (e.g., a P&O reading) indicative of thePRS's position and orientation in the reference coordinate system. Insome embodiments, an additional PRS can be configured to detect one ormore characteristics of the electrical field in which it is disposed,wherein the medical positioning system 316 determines a location reading(e.g., a P&O reading) indicative of the PRS's position and orientationin the reference coordinate system.

Embodiments are described herein of various apparatuses, systems, and/ormethods. Numerous specific details are set forth to provide a thoroughunderstanding of the overall structure, function, manufacture, and useof the embodiments as described in the specification and depicted in theaccompanying drawings. It will be understood by those skilled in theart, however, that the embodiments may be practiced without suchspecific details. In other instances, well-known operations, components,and elements have not been described in detail so as not to obscure theembodiments described in the specification. Those of ordinary skill inthe art will understand that the embodiments described and illustratedherein are non-limiting examples, and thus it can be appreciated thatthe specific structural and functional details disclosed herein may berepresentative and do not necessarily limit the scope of theembodiments, the scope of which is defined solely by the appendedclaims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” or “an embodiment”, or the like, meansthat a particular feature, structure, or characteristic described inconnection with the embodiment(s) is included in at least oneembodiment. Thus, appearances of the phrases “in various embodiments,”“in some embodiments,” “in one embodiment,” or “in an embodiment,” orthe like, in places throughout the specification, are not necessarilyall referring to the same embodiment. Furthermore, the particularfeatures, structures, or characteristics may be combined in any suitablemanner in one or more embodiments. Thus, the particular features,structures, or characteristics illustrated or described in connectionwith one embodiment may be combined, in whole or in part, with thefeatures, structures, or characteristics of one or more otherembodiments without limitation given that such combination is notillogical or non-functional.

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a clinicianmanipulating one end of an instrument used to treat a patient. The term“proximal” refers to the portion of the instrument closest to theclinician and the term “distal” refers to the portion located furthestfrom the clinician. It will be further appreciated that for concisenessand clarity, spatial terms such as “vertical,” “horizontal,” “up,” and“down” may be used herein with respect to the illustrated embodiments.However, surgical instruments may be used in many orientations andpositions, and these terms are not intended to be limiting and absolute.

Although at least one embodiment of a fluorolucent magnetic fieldgenerator has been described above with a certain degree ofparticularity, those skilled in the art could make numerous alterationsto the disclosed embodiments without departing from the spirit or scopeof this disclosure. All directional references (e.g., upper, lower,upward, downward, left, right, leftward, rightward, top, bottom, above,below, vertical, horizontal, clockwise, and counterclockwise) are onlyused for identification purposes to aid the reader's understanding ofthe present disclosure, and do not create limitations, particularly asto the position, orientation, or use of the devices. Joinder references(e.g., affixed, attached, coupled, connected, and the like) are to beconstrued broadly and can include intermediate members between aconnection of elements and relative movement between elements. As such,joinder references do not necessarily infer that two elements aredirectly connected and in fixed relationship to each other. It isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative only andnot limiting. Changes in detail or structure can be made withoutdeparting from the spirit of the disclosure as defined in the appendedclaims.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialsdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

What is claimed is:
 1. A magnetic transmitting element for generating amagnetic field for tracking of an object, comprising the following: afirst spiral trace that extends from a first outer origin inward to acentral origin in a first direction; and a second spiral trace thatextends from the central origin outward to a second outer origin in thefirst direction, wherein: the first spiral trace and the second spiraltrace are physically connected at the central origin to form thefluorolucent magnetic transmitting element; and at least a portion ofthe first spiral trace overlaps at least a portion of the second spiraltrace.
 2. The fluorolucent magnetic transmitting element of claim 1,wherein the first spiral trace and the second spiral trace are formedfrom a continuous piece of material.
 3. The fluorolucent magnetictransmitting element of claim 2, wherein the continuous piece ofmaterial that forms the first spiral trace and the second spiral traceis creased at the central origin.
 4. The fluorolucent magnetictransmitting element of claim 3, wherein the continuous piece ofmaterial is formed from aluminum.
 5. The fluorolucent magnetictransmitting element of claim 1, wherein: the first spiral trace and thesecond spiral trace are cut from a planar piece of material; and thefirst spiral trace and the second spiral trace are creased at thecentral origin.
 6. The fluorolucent magnetic transmitting element ofclaim 1, wherein a first electrical terminal is disposed on the firstspiral trace at the first outer origin and a second electrical terminalis disposed on the second spiral trace at the second outer origin. 7.The fluorolucent magnetic transmitting element of claim 6, wherein thefirst spiral trace and the second spiral trace are configured totransmit an electrical current from the first electrical terminal to thesecond electrical terminal in the first direction and to produce amagnetic field.
 8. The fluorolucent magnetic transmitting element ofclaim 1, wherein: a first plurality of fluorolucent magnetictransmitting elements are arranged in a first plane, forming a firstmagnetic assembly layer; the first plurality of fluorolucent magnetictransmitting elements do not overlap one another in the first plane; asecond plurality of fluorolucent magnetic transmitting elements arearranged in a second plane, forming a second magnetic assembly layer;and the second plurality of fluorolucent magnetic transmitting elementsdo not overlap one another in the second plane.
 9. The fluorolucentmagnetic transmitting element of claim 8, wherein a spacing between acentral origin of each fluorolucent magnetic transmitting element in thefirst magnetic assembly layer and a central origin of each fluorolucentmagnetic transmitting element in the second magnetic assembly layer isgreater than a radius of each fluorolucent magnetic transmittingelement.
 10. The fluorolucent magnetic transmitting element of claim 8,wherein an insulative layer is placed between the first magneticassembly layer and the second magnetic assembly layer.
 11. Thefluorolucent magnetic transmitting element of claim 8, wherein the firstmagnetic assembly layer partially overlaps the second magnetic assemblylayer.
 12. A fluorolucent magnetic transmitting array for generating amagnetic field for tracking of an object, comprising the following: afirst fluorolucent magnetic transmitting element disposed in a firstplane; and a second fluorolucent magnetic transmitting element disposedin a second plane, wherein the second fluorolucent magnetic transmittingelement disposed in the second plane partially overlaps the firstfluorolucent transmitting element disposed in the first plane.
 13. Thefluorolucent magnetic transmitting array of claim 12, wherein each ofthe first and second fluorolucent magnetic transmitting elementsinclude: a first spiral trace that extends from a first outer origininward to a central origin in a first direction; and a second spiraltrace that extends from the central origin outward to a second outerorigin in the first direction, wherein: the first spiral trace and thesecond spiral trace are formed from a continuous piece of fluorolucentmaterial that is creased at the central origin; and an area of the firstspiral trace overlaps with an area of the second spiral trace.
 14. Thefluorolucent magnetic transmitting array of claim 13, wherein thefluorolucent material comprises aluminum.
 15. The fluorolucent magnetictransmitting array of claim 12, wherein: the fluorolucent magnetictransmitting array is disposed within a fluoro window of a magnetictransmitting assembly; a first plurality of non-fluorolucent magnetictransmitting elements are disposed on a first portion of the magnetictransmitting assembly; and a second plurality of non-fluorolucentmagnetic transmitting elements are disposed on a second portion of themagnetic transmitting assembly, the first portion being opposite to thesecond portion.
 16. The fluorolucent magnetic transmitting element ofclaim 12, wherein an insulative material is disposed between theoverlapping area of the first spiral trace and the second spiral trace.17. A magnetic transmitting assembly, comprising: a frame that includesa fluoro window; a first plurality of magnetic transmitting elementsdisposed on the frame on a first side of the fluoro window; and a secondplurality of magnetic transmitting elements disposed on the frame on asecond side of the fluoro window, wherein the second side is disposed onan opposite side of the frame from the first side.
 18. The magnetictransmitting assembly of claim 17, wherein the first plurality ofmagnetic transmitting elements and the second plurality of magnetictransmitting elements are equidistant from a center of the fluorowindow.
 19. The magnetic transmitting assembly of claim 17, wherein eachof the first plurality of magnetic transmitting elements and the secondplurality of magnetic transmitting elements are disposed at a same anglewith a different directionality.
 20. The magnetic transmitting assemblyof claim 17, wherein a fluorolucent magnetic transmitting assembly isdisposed within the fluoro window.
 21. A method for preventing coil tocoil coupling in an array of magnetic transmitting elements, comprising:providing a reference signal to a magnetic transmitting element and alow pass filter in parallel; sensing the reference signal that haspassed through the magnetic transmitting element; generating a directcurrent offset with respect to the reference signal via the low passfilter; generating an attenuation signal by summing the direct currentoffset and the reference signal that has passed through the magnetictransmitting element; and applying the attenuation signal to thereference signal to attenuate the reference signal.
 22. The method ofclaim 21, wherein the magnetic transmitting element is a flat coil. 23.The method of claim 21, wherein the method includes buffering thereference signal via a buffer circuit prior to providing the referencesignal to the magnetic transmitting element and the low pass filter. 24.The method of claim 21, wherein applying the attenuation signal to thereference signal includes: providing the attenuation signal to anon-inverting input of an operational amplifier; and providing an outputof the operational amplifier to a buffer circuit.
 25. The method ofclaim 24, further comprising providing the output of the operationalamplifier to a low pass filter circuit, which includes a first resistorand a first capacitor.
 26. The method of claim 24, wherein the buffercircuit is a second operational amplifier configured for unity gain. 27.The method of claim 26, wherein an output of the second operationalamplifier is provided to a second capacitor, the second capacitor beingelectrically coupled to a fluorolucent magnetic transmitting element,and the fluorolucent magnetic transmitting element being electricallycoupled to a sense resistor.
 28. The method of claim 24, furthercomprising: providing an alternating current reference signal to themagnetic transmitting element and the low pass filter in parallel; andfiltering the alternating current reference signal such that a directcurrent value remains.
 29. The method of claim 28, further comprisingproviding the direct current value to a third operational amplifier. 30.The method of claim 29, further comprising: providing an output of thethird operational amplifier to a non-inverting input of a fourthoperational amplifier; and providing an output of the fourth operationalamplifier to an inverting input of the first operational amplifier. 31.A high frequency fluorolucent magnetic transmitting element drivecircuit, comprising: a voltage input electrically coupled to a modifiedHowland current source, wherein the modified Howland current sourceincludes a Howland operational amplifier with an inverting input of theHowland operational amplifier electrically coupled between a first andsecond modified Howland resistor and a non-inverting input of theHowland operational amplifier electrically coupled between a third andfourth modified Howland resistor, and wherein the voltage input iselectrically coupled to the first modified Howland resistor; an outputoperational amplifier with a non-inverting input electrically coupled toan output of the Howland operational amplifier of the modified Howlandcurrent source and an inverting input electrically coupled to the fourthmodified Howland resistor, wherein an output of the second operationalamplifier is electrically coupled with an output resistor; a phase leadcapacitor electrically coupled between an output of the output resistorand the second modified Howland resistor; and a fluorolucent magnetictransmitting element electrically coupled to the output of the outputresistor.
 32. The drive circuit of claim 31, wherein: the voltage inputis electrically coupled to an input resistor; an output of the inputresistor is electrically coupled to an input capacitor and to anon-inverting input of an input operational amplifier; and an output ofthe input operational amplifier is electrically coupled to the firstmodified Howland resistor.
 33. The drive circuit of claim 31, whereinthe fluorolucent magnetic transmitting element is electrically coupledbetween an output of the output resistor and a ballast.
 34. The drivecircuit of claim 31, wherein an alternating current source is providedby the voltage input.
 35. The drive circuit of claim 31, wherein acapacitance of the phase lead capacitor corresponds with an inductanceof the fluorolucent magnetic transmitting element.
 36. A high frequencyfluorolucent magnetic transmitting element drive circuit, comprising: avoltage input electrically coupled to a low-pass smoothing filter,wherein an output of the low-pass smoothing filter is electricallycoupled to a non-inverting input of an operational amplifier; a modifiedHowland current source, wherein the modified Howland current sourceincludes a Howland operational amplifier with an inverting input of theHowland operational amplifier electrically coupled between a first andsecond modified Howland resistor and a non-inverting input of theHowland operational amplifier electrically coupled between a third andfourth modified Howland resistor, and wherein an output of theoperational amplifier is electrically coupled to the first modifiedHowland resistor; an output operational amplifier with a non-invertinginput electrically coupled to an output of the Howland operationalamplifier of the modified Howland current source and an inverting inputelectrically coupled to the fourth modified Howland resistor, wherein anoutput of the second operational amplifier is electrically coupled withan output resistor; a phase lead capacitor electrically coupled betweenan output of the output resistor and the second modified Howlandresistor; and a fluorolucent magnetic transmitting element electricallycoupled to the output of the output resistor.
 37. The drive circuit ofclaim 36, wherein the voltage input is an alternating current with afrequency in a range from 1 to 20 kilohertz.
 38. The drive circuit ofclaim 36, wherein the fluorolucent magnetic transmitting element has aninductance in a range from 0.1 to 4 millihenry.
 39. The drive circuit ofclaim 36, wherein the low-pass smoothing filter includes an inputresistor, an output of which is electrically coupled to an inputcapacitor.
 40. The drive circuit of claim 39, wherein an output of theinput capacitor is coupled to a ground.
 41. A method for determining anattenuation term for a signal produced by a fluorolucent magnetictransmitting element; comprising: driving the fluorolucent magnetictransmitting element with a first signal at a first frequency and asecond signal at a second frequency to generate a first excitationsignal and a second excitation signal, wherein the first frequency islower than the second frequency; receiving a first received signal and asecond received signal with a computer, the first received signal andthe second received signal having been generated upon receipt of thefirst excitation signal and the second excitation signal with a magneticposition sensor; filtering the first received signal and the secondreceived signal; and determining an attenuation term for the secondreceived signal at the second frequency based on the first filtered andreceived signal and the second filtered and received signal.
 42. Themethod of claim 41, wherein the method includes adjusting the secondfiltered and received signal by applying the attenuation term to thesecond filtered and received signal.
 43. The method of claim 42, whereinthe method includes determining a position of the magnetic positionsensor based on the adjusted second signal.
 44. The method of claim 41,wherein the fluorolucent magnetic transmitting element has an inductancein a range from 0.1 to 4 millihenries.
 45. The method of claim 41,further comprising separating the first received signal from the secondreceived signal via frequency domain multiplexing.
 46. The method ofclaim 41, wherein a frequency of the first signal is in a range from 0.5kilohertz to 2 kilohertz.
 47. The method of claim 41, wherein afrequency of the second signal is in a range from 10 kilohertz to 20kilohertz.
 48. The method of claim 41, wherein determining theattenuation term for the second received signal at the second frequencybased on the first filtered and received signal and the second filteredand received signal includes determining the attenuation term based on:a first voltage amplitude induced in the fluorolucent magnetictransmitting element associated with the first signal and a firstfrequency associated with the first signal; and a second voltageamplitude induced in the fluorolucent magnetic transmitting elementassociated with the second signal and a second frequency associated withthe second signal.
 49. The method of claim 41, wherein determining theattenuation term for the second received signal at the second frequencybased on the first filtered and received signal and the second filteredand received signal includes determining a change in a first positionassociated with the first received signal versus a change in a secondposition associated with the second received signal.
 50. The method ofclaim 41, wherein filtering the first received signal and the secondreceived signal includes filtering the first received signal and thesecond received signal with a Kalman filter.
 51. A non-transitorycomputer readable medium comprising computer executable instructions fordetermining an attenuation term for a signal produced by a fluorolucentmagnetic transmitting element, the instructions executable by aprocessor to: drive the fluorolucent magnetic transmitting element witha first signal at a first frequency and a second signal at a secondfrequency, wherein the first frequency is lower than the secondfrequency to generate a first excitation signal and a second excitationsignal; receive a first received signal and a second received signalwith a computer, the first received signal and the second receivedsignal having been generated upon receipt of the first excitation signaland the second excitation signal with a magnetic position sensor;determine an attenuation term for the second received signal at thesecond frequency based on the first received signal and the secondreceived signal; and filter the attenuation term to provide a filteredattenuation term.
 52. The non-transitory computer readable medium ofclaim 51, further comprising instructions executable to apply thefiltered attenuation term to the second received signal to provide anattenuated received signal.
 53. The non-transitory computer readablemedium 52, further comprising instructions executable to determine aposition of the magnetic position sensor based on the attenuatedreceived signal.
 54. The non-transitory computer readable medium ofclaim 51, wherein the attenuation term is determined based on dividing aproduct of a second voltage amplitude induced in the fluorolucentmagnetic transmitting element associated with the second signal and afirst frequency associated with the first signal by a product of a firstvoltage amplitude induced in the fluorolucent magnetic transmittingelement associated with the first signal and a second frequencyassociated with the second signal.
 55. The non-transitory computerreadable medium of claim 54, further comprising instructions executableto apply the attenuation term to the second received signal by dividingthe second received signal by the attenuation term.
 56. Thenon-transitory computer readable medium of claim 51, wherein thefluorolucent magnetic transmitting element is simultaneously driven bythe first signal at the first frequency and the second signal at thesecond frequency.
 57. A system for determining an attenuation term for asignal produced by a fluorolucent magnetic transmitting element, thesystem comprising: a processor; and a non-transitory computer readablemedium comprising computer executable instructions, the instructionsexecutable by the processor to: drive the fluorolucent magnetictransmitting element with a first signal at a first frequency and asecond signal at a second frequency to generate a first excitationsignal and a second excitation signal, wherein the first frequency islower than the second frequency; receive a first received signal and asecond received signal with a computer, the first received signal andthe second received signal having been generated upon receipt of thefirst excitation signal and the second excitation signal with a magneticposition sensor; determine an attenuation term for the second receivedsignal at the second frequency based on the first received signal andthe second received signal; and determine a position of the magneticposition sensor based on an attenuated received signal, the attenuatedreceived signal having been generated through application of theattenuation term to the second received signal.
 58. The system of claim57, wherein the position of the magnetic position sensor determinedbased on the attenuated received signal is different than a position ofthe magnetic position sensor determined based on the second receivedsignal.
 59. The system of claim 57, wherein: the frequency of the firstsignal is in a range from 0.5 to 2 kilohertz; and the frequency of thesecond signal is in a range from 10 to 20 kilohertz.
 60. The system ofclaim 57, wherein the first excitation signal is less perturbated by ametallic object located proximate to the fluorolucent magnetictransmitting element than the second excitation signal.